Amstaff puppy plays too rough for my min pin?

We have a 3 month old amstaff puppy named Petey. He is a love but his play style with our 2 year old min pin is like play fighting. Petey always goes for the neck and does wrestling. My min pin doesn't like to play this way. He likes to play chase and keep away. However the min pin can't seem to shake Petey, so the min pin is forced to play this way back and he is showing his teeth more and I can tell it depresses him sometimes. I am just wondering if the amstaff will be good to our min pin and our kitty as he gets older? I hear they are dangerous dogs. I was hoping if we raise him right he will turn out to be a good boy. When they play fight too rough I say no, separate them, and make Petey relax to a calm submissive state (like the dog whisperer lol). But I can't seperate them all the time, and they spend the day together in the yard while we are at work. Any tips on raising the amstaff right? Do you think he will be ok with the smaller dog and kitty as he gets older? Thanks!