It might take your brother to set some doable boundaries for her. That your mother wants a relationship with him could be a very powerful motivator for her to improve her behavior. Perhaps he can clearly state some guidelines under which they can have contact. For example, he will not have contact with her if she is rude to his wife, gossips about her to others, etc. If the choice is not being polite to his wife and not having a relationship with her son, hopefully she will make the right choice.

Of course, CareBear, you would need to convince your brother this is a good route to go. It may take him a while to get over being angry at her for being so mean to his wife. A sincere apology from your mother to him and his wife as well as a promise of future civil and adult behavior might be a start...

Good luck.