L.C.
I would have them do EVERYTHING together except for using the bathroom and bathing and sleeping.
Minute they are home from school, they are GLUE! You do homework together, clean together, watch tv together.
So when it's time to watch tv, it's not....I'M WATCHING HANNAH MONTANA...it's....lets decide what we are gonna watch TOGETHER.
Give them 21 days, I guarantee they will stop fighting.
Trust me this works, I've done it. Fighting is always gonna happen, but what a difference it's made in my home when I pulled this on them.
Good luck.