I think the final straw was dad breaking mom's arm.
Your Dad was an attorney who did work for Watchtower when needed, and his behavior toward your Mom was so violent that he actually broke her arm? It wasn't some kind of accident?
I haven't listened to the broadcast on Six Screens (mentioned on another thread) or read anything of this until your posts. I am always shocked when I hear of violence in JW families. It's something I never saw but read plenty about now that I am out.