Still not sure what they're doing with Cap but I wouldn't be surprised to see him in both parts - he did an interview at the end of last year where he said he still had four more films to go including AoU. It may simply be that they're getting around that tricky 6 film contract stuff because they're shooting IW as one film but splitting it in half. Otherwise they'd be missing IM, Cap and Thor from one of the two films!
It's also not confirmed if Evans is leaving because he's mentioned before the idea of maybe keeping the Marvel stuff as his onscreen work and then directing the rest of the time. I think it's all up in the air still (hence why Stan has a nine movie contract because they really have no idea how many they'll need him for) but they'll try to hold on to their big stars for as long as they possibly can. That and I really don't see how they can do Bucky's arc justice in CW with so many other characters and plot lines in it now - it feels like that's going to need a whole other film in its own right!
Back to AoU:
Basically the only thing I find disappointing about the film at the mo is what they've done with Banner. They seem to be mostly retreading his story from last time (doesn't want to be the Hulk, can't control it) and then making him look pretty selfish by deciding he wants to abandon his friends just before a major battle (taking one of their best fighters with him) and then leaving them half way through. That's a pretty crappy thing to do tbh.
Hulk don't particape at the final battle ?