Mother-in-Law Can Do No Wrong?

My wife’s sister has been dating an abusive person off and on for over 5 years. Some of the highlights:

1. He refuses to marry her because he “doesn’t want her to let herself go and get fat.”
2. He cheated on her for 8 months until the girl he was cheating on her with found out about him on social media and contacted my wife‘s sister to tell her about the relationship.
3. After a brief split my wife’s sister reconnected with him and they bought a house together. After less than a year she wanted to leave because he showed her zero affection. No kissing, intimacy, or even an “I love you.”
4. Once he found out she wanted to leave he locked her in the house for 2 days, sleeping in the kitchen so that she couldn’t leave through the front or back door without him waking up.

Eventually we helped her move out and they ended their relationship once again. She then moved back into my mother-in-law’s (MIL) house.

Fast forward to over a year later and my wife is 38 weeks pregnant. My MIL tells my wife that this horrible boyfriend who has been out of the picture for a while will now is back and will be attending all family events, beginning with Mother’s Day.

My wife despises this man and tells her she won’t be attending if he is there. MIL tells her that that she can’t do anything about it because it’s “her daughter’s decision to date who she wants.”

When I first started dating my wife she said that her mom was a bad person. My MIL has never been the best but I tolerated her for my wife’s sake and we made it work.

But now I’m starting to worry about the future of my son and the future of my marriage. My wife and I made up our minds that we just won’t attend any functions with the horrible boyfriend but the greater worry is how my MIL could accept this man back into our circle so quickly.

My MIL shows no remorse when it comes to her decision. She berates my wife and tells her to basically “get over it.” My wife went into labor with all of this stress hanging over her head. Thankfully she had no complications.

The worst of this came when my wife’s 18 year old brother had a graduation party the week after she gave birth to her son. Knowing the horrible bf would be there, my wife scheduled in advance to go to the party 45 minutes before it started so she could take a picture with her brother in his gown with her and our son. Turns out the horrible bf decided to come early and my MIL, the host of the party who is having it at HER house, said she couldn’t stop him from coming early. So my wife didn’t go and never got that moment.

My MIL just plays like she can’t do anything about it, although she will say things like “he’ll cheat on her again” and “he just needs her to move back in with her to help pay for utilities.” She almost gleefully says this stuff but never directs any ire towards the horrible bf. The extended family is super weirded out by him coming back. One of them was upset that he showed up at their house uninvited for a birthday party. My MIL seems to be the only one unbothered by the situation.

My sister-in-law doesn’t say anything about this. She walks around with him looking sad all the time. She’s my wife’s best friend. But they don’t talk much anymore.

And that’s where we are at right now and why I’m seeking help. My MIL is trying to use her new title of Grandma to see our child. We always said we would keep her from seeing our child but at the same time she accepts zero responsibility for taking the side of this guy and gaslights my wife by basically making her seem like the crazy one. Put simply: we aren’t ready to see her at this time and she’s using our kid to guilt us.

Where do we go from here? How do you set boundaries or communicate with someone that doesn’t want to talk about the issue or take responsibility?