I found that finding my own patterns brought greater reward than figuring out those of others. Also, I was reading about a technique today for when someone is causing me a lot of pain - substituting the "she/he/them" for "I" and seeing whether any of the sentences hit any nerves within myself. So often what gets my goat about other people is what I dislike about my own behaviour.
It's a tough situation. And not a particularly comfortable one either. However, your MIL and husband seem to want the visit to happen, so perhaps this comes under the "accept the things I cannot change" part of the Serenity Prayer. The challenge for you is to find ways of finding peace amongst the chaos.
Oh, and your husband seems to have worked out which button to press to activate your fear. Wouldn't it be great of you could deactivate that button by being able to thrive whether he is drinking or not?