B.A.
The way I see it, the fighting is surely annoying for you but it does have great benefits for your kids. They are learning how to disagree with others and resolve these disagreements on their own. As long as they aren't being hurtful to each other physically or emotionally, you need to let them work it out. They are developing very important interpersonal skills that will serve them well throughout their lives. I didn't have a sibling to fight with as a kid, and it shows now that I am an adult.