Very good questions!
A Stage 2 Pokemon evolved via Rare Candy would revert back to its Basic stage if targeted by Espeon-EX's Miraculous Shine attack. The Stage 2 card would be returned to that player's hand, and the Basic Pokemon would be unable to evolve back to that Stage 2 form without evolving to a Stage 1 first and waiting a turn, or using an effect like Rare Candy.
Which leads me to your second question. Under normal circumstances , a Pokemon can't evolve on a player's first turn or during the turn in which it was played, nor can it evolve again if it was already evolved once. This applies to devolution as well- a Pokemon that is devolved cannot evolve on the same turn.
And here's where it gets funky. If your opponent's Espeon-EX used Miraculous Shine, the devolution would occur on your opponent's turn, not yours! That means you could re-evolve Pokemon hit by this attack during your turn, so long as all of the necessary conditions are met (that is, they can evolve normally or you have a Rare Candy to go from Basic to Stage 2, etc).