1 trip there on Thanksgiving isn't going to fix that.

The drunk boyfriend is there 24x7 and has complete control of the situation.

Him showing up on Thanksgiving only means the BF has to wait until he leaves to start being an asshole again.

Not showing up tells his mother loud and clear that he doesn't approve.

This isn't about the BF, this is about his mother.

I've no tolerance for women who tolerate abusive men.

All true. But, there's a lot we don't know... and if this is a situation where she's kind of crying out for help, then he's leaving her in a dire situation. This is about his mother, which is why I'd go ... maybe you leave the kids at home, but I think I still go if I'm him.

Again - lots of back story here that is not known.

Go, but leave the wife and kids at home for Thanksgiving in the evening. Make sure your mom knows she is welcome to come see the grandkids any time, or you will bring them to see her anytime Stumbly McDrunk isn't around. You aren't using the kids to control her behavior, but that you don't trust a man who cusses and shoves women, therapy or not.

Showing your Mom and boyfriend that you can't just be shoved out of the picture will send a nice message.

Curious what your brother's thoughts are on all this?

You're all warm and fuzzy, aren't ya big guy. Again, there's a lot here that we don't know. I'm reading this as a deal where his mom had been married to his father for most of their lives - he died 4 years ago and this may be the first relationship she's been in since then. If so, it's unfortunate that she chose poorly.

I'm also taking a guess here that if that is true - she doesn't have a wealth of dating experience and much like that generation, is used to the guy calling the shots - thereby resulting in her having no freaking clue as to how she might escape this abusive relationship.

If all of that is bullsh and she has a history here... then, sure let her figure it out. But, that's where I'm coming from with my commentary.

I actually went through a similar situation a few years ago with my mother in law. The guy wasn't alcoholic though, but he had mental issues. He didn't work because of it.
They came to visit once and at like midnight he was downstairs making noise so we told him to be quiet, and he started yelling and screaming, so we told him to leave. Her mom sided with him for quite some time afterwards, but we knew the guy and his character. He sort of brought her down to his level. She stopped working and they sat around the house and got fat. We wouldn't go to her house when he was there, and he wasn't welcomed at ours. Eventually, she saw the same things we did and got rid of him.
I think the problem with, "putting aside differences for your mom," is that he can pretend it's ok. If you disapprove then you disapprove. No sense being fake. You can still be nice to your mom - invite her over without him. Go places without him. You don't need to pretend the guy is ok. If he wants to show for a long time that he's a square guy then you change your opinion then.

Good God, it happened TWICE?

Another way to look at this - and it depends on the family dynamics, the relationship you had with your mom and dad - how would your father like you to handle this situation with your mother... his wife?

Consider it from that lens and proceed with caution.

Allow what to continue to happen?

You're an enabler, plain and simple. I'd kindly tell her how to fix her situation, and I'd even help fix it. I'm not going to be around it though, and neither would my kids. This is her choice. A guy like this doesn't change.

Ah, I see. There's definitely a time and place for tough love... depending on the back story, my commentary may change. If there were a history of this with the boyfriends, there's no chance that I'd be there or put my kid's through it.

My first instinct was the "Stick to your guns." and "don't go." response.

Then, I realized that the "if you don't go and he does, then he wins, because he controls her life." response is correct.

I say go, but leave the kids. It lets the guy know that you aren't going to chicken out just because he is there, but it lets your mother know that this relationship has consequences (no grandkids around). Your mom will blame you for not going, but not seeing her grandkids is the REAL and ONLY punishment she will understand.

This way you both stick to your guns and stick by your mom.

The only way him going to Thanksgiving dinner helps her is if she LEAVES WITH HIM afterwards.

Him showing up proves nothing since things go back to "normal" the minute he closes the door.

This.

Abuse.