M.S.
One thing that was hard for me to accept was the day that I realized I was an adult and no longer under my parent guidance but my husbands. That I no longer had to obey my parents but honor my husband.
So, you can stand up to your mother and let her know that as long as she is going to be-little you (much less in front of the children) you and the kids will not be visiting. (I do understand that having grandparents willing to watch you kids is a wonderful thing; however, it is more important for you to set the rules of these visits). I had to do that with my father a few times and let him know if he was going to speak to me in the way he was speaking, we were leaving and would see him another time. I would pack up the kids and go...he would call a few hours later and apologize.
Christians are just humans like everyone else. Hopefully they are trying to live up to the standards set in the Bible. We can never actually do it...that is why God forgives us. To err is human to forgive is divine.
I am sending you a great big hug {{{{hugs}}}}.