My oldest is 7, then a 4 yr old girl and just turned 4 boy (not twins).
My DS7 likes to be in charge, and is constantly having to be reminded not to discipline or try to parent the younger 2. Today I was outside dealing with the tow truck guy, and dd was "walking" the dog inside with a leash. DS had been doing the same thing earlier. Well, he tried to stop her, she refused, he probably put his body between her and the dog. She probably hit him, so he bit her.
He Bit Her!
And this is probably the third time this behavior has occurred in 6 months. Pretty much the same situation. He tries to stop her from doing something he thinks she shouldn't, and it ends when he bites her.
I'd really like to hear your opinions. I'd tell you what I did, but I'm interested in what you would do.