
What made you want to have 3 pups all at once! Seriously, cometiton, or sibling rivalry is normal, and would be kept in bounds by the mother, and other senior pack members, so thats you! You will need to ensure that you can take toys away, and distract the pups when they get too rough. I feel having 3 is not a good thing, as it may mean two ganging up on one.
You should also take each one on its own for training, as being together like this will mean they will bond more strongly with each other than you. Training will also establish you in the Alpha position, and they will respond to you telling them to cut it out. If they won;t shre, take the item away, then offer it back only so long as peace remains, if not away again. You really must be boss if you want to avoid serious conflict between them. In the wild the alph animals would break up any bickering by asserting their authority.