Unless you had a contract or agreement in place before the breeding took place, I really don't see why your neighbor should get a puppy. However, since it's happened, then yes, six weeks is too young for the puppy to be separated from its mother and littermates. The fact that both the puppy and the dam are in distress is very indicative of this. If he insists on having the puppy, at least see if he is willing to wait until the litter is at least 8 weeks (preferably 10 weeks) before taking it home. Also, since they will be living so close to each other, letting the pup spend a few hours at a time at his house, gradually increasing the time, can help ease the transition.