Sisterly love?

I just sit here and listen to the girls play, this last for intervals of about 10-15 minutes at a time rotated in is screaming, crying, biting, pulling hair, and whining. Followed by a time out and a cool down period only to be recycled again in the next 10/15 minutes. Why do siblings love so hard?? I try to help them work it out without getting to the fighting point but sometimes it seems like it IS part of their routine or play. Anyone have any advice? By naptime I am exhausted!!