I should add - my husband recognizes what Eauchiche mentioned above, that he is very lucky to have married into a normie family, and often mentions that he is glad that our child will have a completely different childhood than he did. So, while my husband is working through all kinds of baggage of his own, he is clear on the value of sparing our child exposure to the toxic environment he grew up in.
He has chosen very limited contact for himself also. He would not consider moving to the same city again and rarely takes his mother's calls. When he does, there's often a fight, so now I understand why he doesn't take the calls. We have tried to schedule Skyping with my MIL, but she never shows up. My husband never tells our child that we're planning to Skype with her other grandma so that she can't be disappointed like he so often was. We have promised once and only once that they would getting to meet their other grandma - other than the chaotic visit described, MIL has refused to see us when we've been in town based on various drama, as there always is. After that no-show, my husband adopted a no-mention policy regarding getting to meet MIL.
That's why I don't think he sees what I see in terms of inevitable chaos erupting and us needing to leave it to play out somewhere where our child is not. I suspect he has, after close to ten years of normie family life, started to take normalcy for granted and is harboring hope of more normal family relationships with his FOO. If he did see what I see, I don't think he would even consider inviting her here again.