My brothers wife is psyhotic!?

My brother has been with this girl for about five years. The have a 4 year old, a 1 1/2 year old and another child on the way. They just got married in August 2006. They fight alot, even in front of the kids. When they fight and he wants to leave to cool off for a while, she starts to make threats. One time she said she would kill the 1 1/2 year old if he left, another time she took a bunch of sleeping pills cuz he wanted to leave. And she was pregnant. Also it has recently come to his attention that she cheated on him about the time she got pregnant. She refuses to have anything to do with our family, we don't even get invited to the kid's birthday parties. If we call, she hangs up on us, or if my brother answers, she is screaming profanities the whole time. As a result, I rarely see my brother, and we used to be very close. My family is ready to wash their hands of the whole situation. He doesn't stick up for his family because it only causes more problems.