I've never been in that position, but my guess is that it would be safer to be honest NOW rather than keep your fingers crossed and your eyes squinched shut.
Look at it this way -- either these guys will freak out, or they'll be cool with it. If they're cool with it, you lose nothing by telling them now. But if they freak out, you're WAY better off knowing in advance what's in store, while you still have time to make other plans! If you're worried that they may out you when you tell them, what do you think they're likely to do if they find out after you move in?
Plus, there's some danger in not being able to get away easily, once you've moved in. No, I'd definitely vote for telling them now -- but as I said, I haven't been in that position and don't know what's best for you.
Hugz, ***Jenna***