alliances
 

are you allowed to join a AD guild if your EP,and can you do end game with different alliances?

You can join a guild of different alliance.
You cannot pvp together.
I don't know if you can pve together at end-game, but doubt it can be done before. It certainly cannot be done in any pvp zone.

thanks Vuelhering,i knew about the pvp,but i couldn't find anything on pve.

I don't know why they split factions up for PVE. It would give you a lot more things to do to level as well. I understand how the storylines wouldn't make sense with someone playing both sides, but they could at least make some of the quests available and the zones explorable before veterancy.