<human>: My husband and I are both 31 and have a brand new 3 month old baby girl. We've been together 7 years and married for 2. 

My husbands family consists of his dad and mom (divorced) and 28 year old mentally disabled sister. She is like a 7 year old in terms of her abilities. His parents have a totally deranged, codependent relationship and still live together - ostensibly- for the welfare of their daughter. 

The truth is that my FIL is nasty, unreasonable, prick with whom we had a falling out when out baby was a month old. My husband had always been afraid of his Dad, but fatherhood made him strong enough to confront the bastard.  Today they had it out over the phone, and it ended on bad terms again. This is fine in and of itself because we hate this man and don't want him around our child. The problem is that he keeps my MIL and my totally innocent SIL  away from us.  

My MIL is a very sweet lady who is afraid to live on her own (she could afford it). FIL treats her like utter GARBAGE - less than human- but she takes it so she can have access to her daughter. He has custody. 

If we made nice and pretended he wasn't a total monster who insults everyone around him we could be a big happy family. We tip toed around the man for years for the sake of SIL who loves us so much. We can't do it anymore. 

My MIL has barely seen the baby twice. It's heartbreaking. Part of me wants to give in so she can. 

What would you do? Tolerate the man for the other's sake? Or put your foot down once and for all and let MIL be responsible for her decision to stay with him?

Condense the text into a few key points
<bot>: Evil FIL is keeping husband's mom and sister away from Us because we told him off for being an awful person. Family is torn apart.