I've been having the same problem with our Spunky. He's 7 weeks old from a litter of 3 and he instigates all the time! He's the sweetest dog ever to people, but he's awful towards his siblings! We sold his sister last weekend, and he had the audacity to attack her while the people were deciding which puppy they wanted.
We have decided to keep the two brothers separated when no one is around. We also tell him "NO" when he attacks his brother but that doesn't seem to help. As if little boys listen anyway! Big boys either!
