Just wanted to give you an update.
Spent weekend with mother. Talked about the situation. Again she repeated brother's comment about what goes on in his house, etc. I told her my view and she agreed with me. So she now agrees with both of us, very diplomatic!
What I didn't mention in original post is both brother and sis-in-law have health issues. He's in remission from bladder cancer and has hereditary high blood pressure. She comes from a family with various health issues, mainly diabetes. Also a heart problem (has a stent) and on thyroid medication.
According to my mother, there's going to be some developments as a result of the incident. I now feel more confident that there will be an apology, then I'm not holding my breath!
Then I'll deal with the assumptions made about me by family members and the derogatory comments. Decided not to tell mother or aunt the unacceptable ones made about them by sis-in-law. Believe she would only deny it.