That message was seen and heard by everyone in both universes in the DC Versus Marvel #1, as was their command to have super-beings from each universe do battle, because in their battle centuries ago, some of themselves wound up in each others universe, and each brother desired to be whole. Whichever universe had more victorious champions would continue to exist. The universe that lost the most matches would vanish forever, and thus the Brother whose universe wins becomes whole once again. However, the champions can not refuse to do battle, for if they didn't then The Brothers might, would, go to war themselves. And if they did, then the vast energies they wielded would once again destroy everything in existence.
When it was time for champions to battle, The Brothers would summon them to their specific battlefield, and the champions would battle until one of them was at least immobilized. While the battles were going on, Access and the old guardian were trying to figure out how to save the universes. However, the battles were over before they could come up with any plan. When the battles were over, it was a draw, and the universes merged. Before that happened, Access stored fragments of the Brothers in Captain America and Batman to restore the two universes, but he had to defy Dr. Strangefate, who didn't want that to happen.
The old guardian had thought The Brothers had merged and settled the contest in their own way, but he was wrong. Spectre and Living Tribunal were holding the universes together to keep The Brothers from destroying one of the universes. He also managed, with some help from Spectre and Living Tribunal, to get Super Soldier and Dark Claw near where Access was. Then Access was able to give Spectre and Living Tribunal access to the fragments, the power, he had stored in them before the universes had merged.
After the universes were restored, The Brothers did what everyone feared they might do...They did battle. They had a fight as fierce as the one they had centuries ago, and the energies unleashed threatened to do the same thing they did before.
"Throughout his existence The Spectre has been master of many things. Space and Time, godlike power... but with his comment to The Brothers' state of mind, he has mastered something new. Power is unleashed that none have ever witnessed... and The Spectre and The Living Tribunal are awed."
That passage described the battle of The Brothers. Their battle made the sky itself back on Earth "bleed." The Spectre and The Living Tribunal tried to stop them, as did Access, Batman, and Captain America, but to The Brothers they were "dust motes with attitude."
The Brothers eventually, at the point when their swords collided with fantastic power, unleashed the energy that would destroy all. Batman's and Captain America's cores were rent asunder, but at that moment, their lives flashed before their eyes, and the eyes of The Brothers'.
Those stories calmed The Brothers. They realized "that they who encompass the whole of reality...have become smaller then the smallest of their components." Then, for the first time in all history, The Brothers spoke. And they both said "You've done well." It was those three words that saved two universes, and restored peace.
Powers-The Brothers are vastly omnipotent. They are the mightiest beings in all DC or Marvel, far exceeding the Spectre or Living Tribunal. Their true power can not be described, but it was enough for them to easily destroy two universes. They wield two swords, each of which channels The Brothers' limitless power.
While obviously not all of their powers have been shown, the ones that have been are:
All of these are at an unfathomable level, as are all the powers they can be assumed to have, since they are at the highest omnipotence level of anyone in the DC or Marvel universes.