I think a little robx is needed here. Don't tolerate that abuse. You need to stand up to her and make it clear that you will not be her punching bag, physically or emotionally. If she can't discuss things rationally with you, refuse to be in the room with her.
Talking to your W's family may have been a tactical DBing error, but it wasn't some horrible offense. You are trying to save your M, and wanted their advice and support. Hardly a capital crime. Your W's reaction is due to her overwhelming guilt.
