[lil fu fu girl]

I have two, 4.7lbs & 7.4lbs. The little one does, once in awhile try to pick on the bigger one who is younger than her. When the picking turns into fighting, I let out a loud screech, and then grab the little one and put her into her kennel. Usually the loud screech is enough to freak them out and it stops. However, in the kennel, she has quite time by herself. Which she hates! She has begun to associate the screech and "time-out" with her behavior, and her "picking" has begun to subside substantially.
Good luck with your two...I swear they are just like children....