Keep an eye on your pups and seperate them if they get too rough. It is almost time to start seperate obedience classes. It may be normal for dogs to wrestle for dominace, but not until one is bleeding. I have seen mother dogs kill their own puppies who are getting too much attention. People think it is great to keep one of the puppies or to get two pups from the same litter, but serious rivalries do occur. Mounting is a form of dominance at this time in their lives, but I hope you plan to get one or both neutered as it is not uncommon for the brother to become the father when they reach sexual maturity.