A. You are correct in thinking that this aggressive behavior between your puppies is something you need to address immediately. When normal puppy play behavior (growling, teasing, wrestling) escalates to aggression (snarling, inflicting wounds), you have a problem. Unfortunately this occurs frequently when siblings are raised together, although it is more common in siblings of the same sex. For this reason many breeders do not allow siblings to go to the same home.
You have recognized that it is important to separate the puppies when they fight. Each time a serious fight occurs, it damages their relationship. Now you need to focus on preventing the fighting. There may be triggers which you can avoid, for example by feeding the dogs separately, providing duplicate toys, and having one person pay attention to each dog at the same time. Some triggers you cannot avoid, for example fighting over status (dominance). For this reason the puppies should not be allowed to interact without supervision. Crate training is an excellent idea so that the puppies are not left unsupervised together at any time. When they interact, they should be given lots of rewards (treats, kind words) for calm behavior. In a more controlled environment they should be able to work out their dominance order without resorting to full-blown fighting.
These are only basic suggestions - there are lots of tools you can use that are specific to your own situation. An excellent reference for these tools is Ian Dunbar's "Before & After Getting your Puppy." You should also consider puppy training class (separately, if at all possible). And of course, I would have your puppies spayed and neutered as soon as possible, to remove the hormonal influences on their behavior. If you feel the problem is overwhelming, I would not hesitate to contact a behavior specialist. Ask your veterinarian for a recommendation - there are lots in the Bay Area. It could make the difference between keeping both your puppies or having to find a new home for one of them.
--Dr. Heidi Strand is a veterinarian for the East Bay SPCA in Dublin. She has lived in the Tri-Valley for 10 years with her family and an assortment of four-legged friends. Questions can be mailed to 315 Diablo Road, Suite 100, Danville 94526; or e-mailed to email@example.com. Her column runs every other week.