It is very seldom that you will come in and only do one role. Usually, you will do two or three. They will separate them throughout the game. With a game like Assassin's Creed, you have 40 or 50 hours of playing, so if they space the characters out properly and there's 10 hours in between, no one is going to recognize that there are some voices doubling up.
On November 6th, 2012. See this statement in context.