We have the same family! They are identical! Except my RAH doesn't have an older sister. His mother is the queen enabler, his father is an A, and his brother is an A. RAH is always looking for approval from his brother. For some reason, looks up to him, even though he is unemployed, divorced several times, and drunk daily.
MIL is supportive of me as long as I am playing the game and pretending to be happy in my marriage, something she has done her entire life and has taught her son that it is a "good" wife/mother's responsibility to do. For better or for worse, right? If I choose to distance myself from their dysfunction once in awhile and maybe go do something for myself while RAH has the children over at their house (the only time I get to myself...when he goes to his parents.....because his mother will watch the kids for him while he relaxes) she will give me the cold shoulder and not talk to me. They are sooooooo dysfunctional and yet my RAH thinks it is normal because it is all he knows.
I feel for you WTBH, it is a very difficult position to be in. I am so proud of you for standing up to you mil. I am sure my day will come.