Does he nip when he is only on the floor? Or is it when he is in the hands of one of its owners?
How old is he?
Does he do this with all people including the people he lives with?
Does he growl, show his teeth, or get really silent before he does it?

You need to let the puppy know that mouthing/nipping is not acceptable.
If the dog is in its owners hands when puppy goes to nip simply say "eh eh" from the bottom of your stomach ( your serious voice) and then put it on the ground right away. Ignore it for a while so that it realizes that you are not going to put up with that.
If the dog is on the floor, do essentially the same thing. say "eh eh" or "ieee" in a high pitched voice ( like its litter mates would do if it went too far) then either cross your arms and ignore or get up and leave. You have to make sure that everyone is consistent with the training or else puppy will get really confused.
If puppy is not doing it because it is playing then it could be getting scared of people being such a little dog it can be scary for big people to reign over you and start petting you. If this is the case try approaching the dog sideways, getting down to its level, and then letting it come up to you. If you do this enough puppy will understand that big towering people are not here to hurt it. Another thing that you can do is have some treats handy. Once you approach the puppy correctly if he comes up to you and lets you pet him with out nipping he gets a treat. Try this with new people too, that way he begins to think…if I go up to these people and let them pet me I get a wonderful treat. This will also help puppy socialize properly. Another thing is if the puppy is nipping out of fear than make sure to nip it in the bud while he is still young.
I hope this helped let me know if there is anything else that I can help with, or anything that I might have missed.