Your puppy is just that - a puppy! Puppy's nip - especially if they were taken from their litter too young. What you need to do is teach him bite inhabition. Anytime he bites someone, you say "Ouch!" (make it sound like a puppy yelp) and get up/move away. This will teach him that biting you (or your sister or brother) gets him an undesirable response - no attention. You have to do this evertime. "Ouch" and then leave puppy alone. Turn your back on him. If he keeps nipping at you to get attention, remove yourself from the room (or step behind a dog gate). A little while later, go back and give puppy attention. If he nips again - do these steps again.
In NO TIME your puppy will get the message. It's worked for all my puppies.
