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?
"I don't really think there is a need to raise or debate this point."