I hear you!!! My two daughters did nothing but fight. I was convinced they hated each other. If they weren't screaming at each other, they were physically beating each other. It was horrible!!
I resorted to sending them to their rooms (hooray for separate rooms) for one hour when they fought at home. When they fought in a store or somewhere public, they were sent to their room for the night when we got home no matter what time of the day it was. If they fought in a restaurant, we left whether our food had been delivered or not. Any other place, we would go outside to have a "discussion", then we went back in and tried it again.
Eventually, it became almost bearable and today they are close friends.