WTBH-
I missed this post yesterday, and because I don't have kids I wanted to comment about something earlier in the post.
Last week with my therapist I had a discussion about the crazy stuff my ex was saying about me.....and did I have to believe it.
We ended up talking about how some of that crazy stuff said (like what you MIL and husband said to you about this situation) is a way to deflect attention from the real issue....the drinking, his behavior etc. In a very real sense it made me a scapegoat, and I took it on....repeatedly. If it worked once why not continue to try it.....
Though I like my ex-MIL pretty well when I saw her at Xmas time (ran into her at the store) we had a talk about something non-ex related that made me realize she had no idea about the reality of my life now or then. She is still in the level of denial I was for so long before I started to get help.
That is not to excuse her. It was a help for me when I realized this...because then I don't have to take on what she says of thinks.
Just my two cents on the rest, but to me if feels like you are not getting a whole lot in return personally when you are worrying about your husband's family and their relationship with yours.