Elderly mom is verbally/emotionally (& now possibly physically) abusing dad- help?

Thanks so much for sharing this situation! My elderly parents are are going through a very similar situation. Mom has always been extremely verbally abusive! I'm worried though...today dad called to say she went absolutely crazy over a minor and easily correctable mistake he had made...he said she was completely out of control and yelled '10x worse than usual' & that is scary. Dad is 85 and frail...this is the first time I know of, that mom has been physically abusive. Her verbal abuse has been escalating for years. Mom has always been angry and unhappy and takes it out on others. She seems depressed but won't admit it and absolutely refuses to talk to her doctor about her feelings and blames EVERYTHING on dad. Ironically, she cares a lot about what others think...I suspect she doesn't want the doctor to think less of her. She goes to great extremes to present very well at her medical appointments and be seem perfect. It seems she cannot control her emotion/impulses anymore when it comes to dad...& somehow in her mind genuinely does believe he is the cause of all her grief. She was a stay at home wife & always has had a good life, comfortable home, very nice clothes & car & no financial worries, yet she is deeply unhappy & refuses to talk about it. My brother is also an issue. He's like mom. Yells and screams at everyone and everything and constantly in a bad mood and blaming everyone but himself. He refuses to talk to me and has blocked me from texting or calling him...I've tried to reach out to him for years in the hope of building an understanding. He keeps his office at mom & dad's house... and often yells at them both when he's there. A few months ago, the neighbors called to tell me that they were going to call the police next time they heard him screaming at dad. The neighbors call him the 'abusive son' of my parents...yikes! I had been living overseas for many years and returned a few years ago hoping to better understand the family situation here and be of help...sadly, nothing I've tried so far has improved the situation...luckily I have wonderful support from my friends. Any insights or suggestions on how best to deal with this would be greatly appreciated! Thanks!!