Concern about Family living with Suicidal Parent

I'm not sure where to start and I definitely do not profess to know the answers. Who really does? My brother in law is suffering mental illness and there are two children involved and his partner. His brother is also trying to support him. This has been going on for well over two years but has escalated over the past two years and even more so recently. There has been verbal aggression towards his partner and threats of suicide if she leaves. The children are scared as his moods are unpredictable as is she as she has become his verbal punching bag. He keeps saying he knows what he needs to do and blames it on being tired and not taking his medication. I'm really concerned that the guilt is what he might do is pressuring everyone involved to keep the family together. But what about the mental health of his partner and children. One of whom pulls out his hair and is soiling himself. This has been going on for quite a while. I know his partner is sacred and torn between what will happen if she leaves. I very torn right now as I don't feel she and the children should be in the same house as my brother in law. His brother is up and living with them but obviously this can't go on as he has a family who needs him too. So what happens when his brother is not around to help keep him calm...back to his partner being verbally abused day in day out for not saying or doing the right thing. She is socially isolated as are the children.