how old was he when you brought him home?
puppys use their mouths to play, the beast thing to do is remove him if he is getting to rugh, just tell him no pick him up(do not pet him) and put him out the room for a minute. bring him back in and repeat if nesissery.
is this your first dog?
to be honist you going to have to get used to them playing like this as they will most likely do it for the rest of their lives, it just looks rugh because the 7week pup is yonger and isnt able to play on the same levle.
you are also going to have to spend alot of individual time with each of them on their own, even though theh are from different litters you are going to have the same problems with them over bonding or becoming agresive to each other as if they were siblings in the same home.
the 7 week pup should realy still be with its mum in my opinion, and if you got the other pup earlier than 8 weeks then this has also been because the pup has not had time to learn how much is too much for biting.
remember, its your home, you are pack leader, you decide when the game ends. you need to teach him what is acceptable and what is not. it will be easier when the yonger is a little older.