Magneto: probably.  He can use magnetism to do silly things, so why not?  He'd probably control the iron in their blood to slow the flow of blood to the brain so they couldn't function properly... or something equally long-winded as that ;) 
 
Apocalypse:  I'm fairly sure he can, but I can't recall any instances of intangibility/phasing. 

Magneto: Depends on the teleporter. For instance, Nightcrawler navigates along lines of electromagnetic force (similar to the way birds and fish navigate when they migrate) . Magneto has been able to sense when/where Kurt is about to appear, and even reroute Kurt to appear somewhere else. However, a teleporter like Magik he wouldn't be able to do anything against.
 
But as Xerox-kitty has said, Magneto has also cut a mutant off from their power by manipulating the bioelectic signals between the nueron's in a person nervous system. He's actually frozen the entire group of X-men (from all the books)  inplace this way.

In Uncanny #150, he zapped Kitty with electricity when she tried to pass through him and nearly killed her. As long as it can conduct electricity, it's vulnerable to him.
 
And given that Apocalypse is riddled with nanotech. He is *especially* vulnerable to Magneto.

Would forming a magnetic field around the teleporter affect their teleportation ability?

Like I said, it depends on the teleporter and exactly how they do it. Kurt is opening up dimensional gates, so I could see where manipulating the EM field might have an effect. I mean Magneto has opened up traverseble wormhole. I don't know how similar wormholes and dimensional gates would be, you'd need a physicist for that, but I can see where they *could* be similar. 
 
Doing a quick check, I see that Magik and the Vanisher also are opening dimensionl gates. I think given that Magneto has affected Kurt's ability to teleport, given enough information/encounters he might be able to affect Illyana and Vanisher as well.
 
Though Illyana has magic to protect her, which Magneto is vulnerable to/has no affect on.

" Like I said, it depends on the teleporter and exactly how they do it. Kurt is opening up dimensional gates, so I could see where manipulating the EM field might have an effect. I mean Magneto has opened up traverseble wormhole. I don't know how similar wormholes and dimensional gates would be, you'd need a physicist for that, but I can see where they *could* be similar.   Doing a quick check, I see that Magik and the Vanisher also are opening dimensionl gates. I think given that Magneto has affected Kurt's ability to teleport, given enough information/encounters he might be able to affect Illyana and Vanisher as well.  Though Illyana has magic to protect her, which Magneto is vulnerable to/has no affect on. "

YW. :)

Without outside assistance, Apocalypse cannot defeat Magneto. Part of Apocalypse' molecular make up is nanotech. Magneto controls electromagnetism, which means he has absolute control of the material Apocalypse is made of and the energy it runs on. Apocalypse is a sitting duck.
 
They already had this showdown at the end of AoA. Magneto ripped Apocalypse in half.

Magneto was depowered in "The Twelve" storyline. He was relying on Cortez for energy boosts and his lack of power is what made Apocalypse's machine fail.  When he finally tapped into Polaris abilities, he kicked butt.
 
You can think whatever you want, I have comics and science to back up my side of the argument.  Electromagnetism is the force that holds all matter together, it is one of the most prevelant forces in phsyics. Any tech that Pocky throws at Magneto, Magneto has control over. If Apocalypse has a couple years prep, then Magneto gets a couple years prep. I would say on equal footing, equal prep, Magneto has the advantage, especially since Apocalypse IS partiality metal and runs on electricity and Magneto has a natural ranged attack. As Xavier once said, Magneto "has one of the most powerful mutant abilities ever to manifest itself." He is one of the most powerful beings walking the planet. He is a step below the Silver Surfer and has defeated the Phoenix. And Magneto ALSO has access to extremely advanced tech that is a combination of all the alien races he has encountered along with his own created with his own unique perspective. According to one writer, Asteroid M contained technology, "Reed Richards would envy.'  Not to mention the guy is a tactical genius known for taking out teams on a regular basis.
 
I'm not saying it would be impossible, but Apocalypse would have one HELL of a time taking him on when he is fully powered.

" @Pania:  I know about the science part.  1. So Magneto can control Apocalypse's Celestial technology?   2. So it does not matter that Apocalypse is more intelligent than Magneto and that Apocalypse has energy absorption, can teleport, can make himself intangible and has complete control of his body on the cellular and molecular level and has a healing factor?    3. Apocalypse can basically turn himself into anything that he wants to, right? Including something that is not metal?  Also, Apocalypse has nearly limitless strength and can grow to a nearly immense size. Does this matter? 4. Magneto defeated the Phoenix? When and where? Do you happen to have scans?   5. I heard that Magneto's shield also protected him from Galactus', and Thor's attacks. Is this true? How did he accomplish these feats? It seems to be a little bit far fetched.  Correct me if I am wrong though.  6.  I don't think that Apocalypse was at full power when Magneto defeated him in AOA.  Don't forget that Magneto and Apocalypse fought only twice in the AOA. In the first battle, Apocalypse won easily. In the second, Magneto obviously won.  Magneto won because good guys always win.  "

Because this has obviously become battle thread. You don't seem care about the answers, you just want to prove Apocalypse can beat Magneto. Even though I have given you PLENTY of evidence that proves that it would be EXTREMELY difficult for him to do so you continue to argue about it and in the course of which you either ignore things I have said or  pointedly refuse to understand. There is a point where people lose patience with answering "questions" when the person asking is not listening. You do not seem to want to know that Magneto is in fact more powerful than Apocalypse.
 
3. If you understand it so well, why do you keep questioning it? You keep asking questions that are answered by that fact. I give you multitudes of examples of the feats he has accomplished which include playing around in the fabric of time and space and you ask questions like you do not understand these things.  If you would just stop and think about what you know and what you are asking I might get a little less annoyed.
 
(BTW-This is also a trait that is handy with college professors. In college you will learn that there is such a thing as a "stupid question": It's the question you ask that you already had the answer to if you just thought about it for a sec.)
 
4. One of the traits all Omega class mutants (such as Jean Grey and Iceman) have is that they have transcended their physical from. Magneto appears to be on the edge of the same transition, he has actually lost physical mass when he has lost reserves of stored EM energy (Uncanny X-Men #275, X-Men Vol. 2 #3). In fact in X-Men: The End Claremont showed Magneto evolving into an energy being.  He has not done so in 616 continuity yet, but the potential is there.
 
As for how he defeated the Phoenix: What the text said is that he created a "bottle effect" and drained of her energy, the picture pretty much showed Phoenix with a field of energy around her and her energy flowing out the top. The only copy of that issue I have in my collection that I can find is graded and encased so I cannot give you that scan. I probably have another copy in a reprint (Like Classic X-Men) but we are talking about shifting through 8 long boxes worth of comics to find it. 
 
But here is the synopsis from UncannyXMen.net:
 
" He feels optimistic, as there is only Marvel Girl to keep him from total victory. “First off, Magneto, the name isn’t Marvel Girl anymore!” says Jean as she assaults Magneto on myriad levels of psychic and physical power that rivals Xavier’s. “It’s Phoenix!” As she stands before him with the Phoenix Force around her, Magneto is forced to the ground. “Good god,” he says in disbelief, unsure where all Jean’s new power has come from. Jean’s attack is impressive and Magneto begins to falter under sustained pressure. She feels confident and asks how he hopes to stand against one whose power is born of the raging sun itself. 
 
Suddenly, however, there is no more power left and she finds she has reached her limit. She didn’t even know she had a limit. As she falters, Magneto uses the magnetic bottle effect he’s created to draw the life-energy out of Phoenix like a sponge. Behind him, Wolverine rouses, rubbing the back of his neck. He sees Magneto putting the kibosh on Jean and it looks like she’s going down for the count. He stands, despite his pain, as Magneto proudly exclaims that eight of them entered his domain and eight of them have gone down to defeat at his hands. "
 
And the link.  
 
And if you want to know the scientific plausibility of such an act, again you can refer to my essay here. Specifically this part:
 
"Magneto should also be able deflect the solar winds (perhaps a variant of Marvel’s nebulous “cosmic energy”) as the Earth’s own magnetosphere does. He should be able to shape the northern/southern lights, which is the solar wind reflecting off the atmosphere at the poles (a rather romantic image). Because the solar winds travel along magnetic clines of force, it is theoretically possible for Magneto to shape and focus that energy and matter into something more damaging."

If that does not satisfy you, I'm sure there are a number of people here who can provide a scan.

5. He used his own, natural, electromagnetic shields. What answer were you looking for?
 
6. The AoA Battle in which Apocalypse defeated Magneto and Bishop? Took place in The Amazing X-Men #3, and he did so with the help of an entire team of Infinites and the Vanisher. And the only reason Magneto stood down is because Apocalypse was holding his son hostage. As soon as Charles safety was assured in X-Men: Omega...well, then Daddy took the gloves off and ripped Apocalypse in half. 
 
Now that, I *do* have those issues handy for scanning. 
 

" @Pania: I never denied the fact that Magneto is more powerful than Apocalypse. Battles do not always go to the more powerful. Emma Frost defeat Rachel Grey.  The latter was more powerful, but not as skilled and experienced as Emma.    LOL. Thanks for telling me. Yeah I am a Junior in College so I already know about that. But are you my college professor? I don't think so. Also, stupid is a subjective term.  What you consider to be a stupid question may not be a stupid question to anyone else.  Thanks for your opinion though. LOL. Just wanted to let you know.  Thank you for actually answering some of my questions.  I am impressed.  I do appreciate the explicative answers.    For 5. WOW. That was a great answer. Very elaborate indeed. Thanks again.  6. Again, you failed to address the fact that X-Man severely weakened Apocalypse before Magneto ripped him in half. Was Apocalypse at full power then, in the AOA?   Also, I am not a fanboy of any character really. I see myself as neutral.  I just ask a lot of questions, as you may have noticed. You made the wrong assumptions about me. Thank you for that. LOL. "

" @Pania:  Hello.  I never know "LOL's" were cute. LMAO. Maybe I should show them to my girlfriend.  Anyway, enough with your Homo sapien complexity.     5. I am looking for an explanation as to how Magneto did this. Did Magneto use candy to defend himself from those attacks? Or did he use chicken tenders? Try to please explain what was going on. For instance, Magneto's shield withstood Phoenix's attacks because of the "bottle effect" explanation. Try to give an answer like that if you can .  6. That is my point as well. X-Man was not even able to defeat holocaust. That is pathetic.    What exactly were holocaust and Apocalypse doing to Magneto, while Magneto was being held by Apocalypse? How exactly was he being tortured? Why didn't Magneto fight back?  Would it make a difference if just Apocalypse had full prep that lasted a few years and Magneto had no prep at all?  No teams. Thanks.            %Pr "