How do I handle rudeness, irritation, and anger expressed by my 89 year old mother towards my 95 year old father?

This has always been a problem in my parents lives and this abusiveness has extended to me since childhood. I have had to stay away from her a lot because of it. But now that she has nerve deafness and he has lost much of his hearing, this abusiveness is getting much worse. She orders him around, corrects him angrily. He is a gentle person who does not fight back. This abusiveness at times is directed at me as her daughter. Even when I talk to her about the abusiveness she admits she shouldn't be doing it but that doesn't seem to change her attitude toward him. I was told by a caregiver who came in for 3 days recently to help, that he should be taken out of the house on shopping errands and drives as often as possible by my sister or myself to get away from her. How can I (we) help her? We are exhausted from giving 24/7 care recently as she was very ill and need to have outside help. We feel a caregiver is best at this point. Would appreciate any insight.