Should we cut them off?

I don’t know what’s up with my in laws, but my MIL has some mental issues. My FIL gets so stressed and frustrated by her that he kind of goes off the deep end sometimes too. My MIL will be perfectly normal and happy and kind for months at a time, and then something happens that she doesn’t like, she gets crazy for weeks or even months. When she found out about my husband dating me, and she met me, she told him I was too fat (literally her only problem with me) and then went crazy because he wouldn’t dump me. She would call randomly and yell at him, then stew over it for a few days and then call and yell about something else. She did this for months, saying that he doesn’t exist to her anymore. She even burned almost all of the pictures of him as child. Then she’d just stop talking to us for months.

Anyway, we thought she was doing better. We’ve been married for 3 years and have a 2 year old. She’s been nice since shortly after our son was born. After not speaking to us for over a year, she called my husband up when our son was born and acted like nothing ever happened. They started to visit (we live out of state) and stay at our house for 1-2 weeks at a time, and we all seemingly were getting along. But then we told them were expecting another baby, and she has lost her mind again. She won’t explain why. She has no real reason to be upset. We own our home, we make plenty of money, and we planned this. But she’s still mad about it. The only thing she has to say is that we “can’t handle the one we already have” because he isn’t potty trained yet, and she thinks he should be, which is bullshit. She tried to convince my husband to leave me and move back home because she could raise my kids better than me.

I just think it’s time to cut them off. I’m so hurt by the fact that won’t be happy for us. We told them about the pregnancy a week before our sons birthday and they didn’t even bother to call and say happy birthday to him. He’s their only grandchild right now, and they didn’t even care.

My FIL is mad at us about it too, because he has to deal with her when she goes off. He thinks everyone should avoid doing anything to set her off, so he blames us. Should we cut them off?