I have a 9 mo old pug and we just got a 2 mo old pitbull mixed with lab?

we got the pitbull from a friend the friend had other dogs 2 weiners the weiners were kind of aggressive. now the friends son came to check on the weiners and pit but didnt put them in their respective cages they just left them out so the puppy had to fend for himself until we got their (the friends house) when we bought our dog otis the pug he was nipping at him and bellowing at him. so we figured the atomsphere at the friends house was to much for him and it was causing the behaviour towards the pug. so we took the puppy home home to see if he cooled off from the atmosphere... so today came and we let them attempt to play with each other but the same results happened it was ok at first then it got a tad bit out of control the puppy trying bitting an bellowin at each other it even got to the point where their fir was standing up on their backs. now i dont know much bout pits but i no the terrier breed is a bit possesive and territorial and head strong but is this natural behaviour for a puppy. now whe had the pug when he was a puppy but it was just him no other dog plz help. oh b4 i 4 get the pit is pretty calm when it is by it self