Wow, things become so much more complicated when you're dealing with pregnancy hormones.
I just had a little myself so I completely understand. One thing I wasn't sure of. Does your mother-in-law live with you? If she does, first don't ever leave your kids in her care. You teach them to do as you say and to stay put where you want them to be. This takes consistancy. They will learn and obey.
If she does not live with you, spend very limited time with her. If has an obvious condition that is going untreated then you will not be able to blame her if an accident occurs. Normally, I would say to work on the relationship and give tips BUT you are pregnant.
I've also found that men do not know how to handle conflict between thier wife and mother. My thought "He married you" that is where is commitment ought to be. He is also the provider and protector of his family. He can protect his family without dishonoring his mother. Setting boundaries for your family is okay.
You and your husband are not responsible for her feelings. If she gets mad or sad, what's the worse thing that could happen?You and your husband are responsible for your children. Sometimes working with the child is more effective than trying to work with the adult.
We used to visit some relatives weekly. There was one adult that would offer my kids candy and do magic tricks to lure them into another room without me or my husband's knowledge about it. (Scary) I usually found them or one in his room playing games or watching a video.
I had talks with my kids about staying out of the room and letting us know when he would approach them. In essence we set rules for them but did not tell them bad or scary things about him.(Honoring him) They still wanted to play and that was okay as long as it was in front of me!
K.