Well, I have been trying to finish reading this thread for over a week now and I just never seem able to. But finally I did... and I am glad that you worked out the birthday problems with your hubby. Communication is key!
Oh, and a very happy birthday! (however belated it was...)
I am so sorry to hear about the problems between you and SIL. She sounds immature and unresponsible. I think you should definitely sit everyone (hubby, Bro, SIL and yourself) down and talk things out. You might mention that the situation is making you resent them, and you don't want that. I am sure you want a good relationship with them and their living with you is making that impossible. Good luck though! I hope all works out all right!