Hi J.,
I know this is a very frustrating time, I also live in a very small house, actually my two year old daughter and 4 year old son share a room right now. (we are looking to move soon), however, he is playing a power struggle with you now, because he knows that he is getting his way. Did you ever watch the Super Nanny, She is fantastic, she has alot of helpful tips, watch the show and get her book. She suggests and I Know it works to just put him to sleep as usual, and when he does scream go back in and explain to him that he needs to go to sleep, put him back in his bed, every time he does this, just keep going back in and putting him back after the first time going back in do not say anything to him and just keep doing eventually he will get the hang of it. It will be very frustrating and hard on you and your husband it may take and hour to two to get him back to sleep, but after a few days he'll get the hint that he is not going to win this battle. He needs to learn this you may have a rough couple of nights, but it does work. If your 4 year old gets up my suggestion is to just reassure him everything is fine and try to get him back to sleep. I hope this helps. Also, do not yell, speak very calmly to him, if you knows he's getting the best of you, he'll keep it up even longer, because he knows he's going to get his way. Good luck.