I'll chime in here if it's okay. I'll tell you what I'd do if I were faced with the situation of taking care of a pup that age if unable to get it back with it's litter mates. What I'd do, as it was mentioned is teach it what it learns from his littermates and mom (as was already mentioned but I'll reiterate because it's so important). Bite inhibition: It's important not to scold or be very harsh in response to puppy biting. Biting and rough play is absolutely normal and acceptable in doggie society BUT there is a limit. Dogs don't know that human skin is very, very fragile. When the pup bites anywhere close to causing pain, I'd give a quick, high pitched squeal (not so loud as to cause him to cower) and end the attention immediately, turn away, walk away, whatever....but playtime with humans is over. Then try again in a minute. If he mouths gently, let him...show him that gentle mouthing works to get attention and affection. Repeat every single time. (There will be a lot of jumping up and down from the couch and walking away. Plan on it. It will go on for some time)
Later, once he gets this down (which will be a process of both learning and maturity) you can change that gentle mouthing to happen only upon invitation because it would get obnoxious if he did it all the time. You change it by reinforcing/rewarding for the gentle mouthing upon cue and walk away for gentle mouthing without being invited) But while learning to regulate his bite pressure, allow very, very gentle mouthing. The ending of playtime, affection etc must come immediately upon even close to painful biting and it must happen absolutely consistently. Speaking to the pup....even a "no" or pushing him away, holding onto his muzzle...any further attending to can be perceived as attention (any attention is better than none) so that can get in the way of learning. Everyone must do the same thing who interacts with him. One quick ouchie squeal and walk away or turn your back.
Another thing he's missing out on by not being with littermates is learning tolerance for frustration. He's learned some since he was with them for a while, but it needs to be continued by humans. Littermates push and squeal at eachother, fighting for a nipple. One gets pushed away one minute, another one gets squeezed out another time. The same thing goes for other things; attention and grooming/ bonding from the mother. They push and squeeze, step on eachother, clamor around. What humans can do is try to emulate this but being VERY careful not to over do it. That's important. Once or twice while he's eating or sleeping a gentle pressing away just for a 2 or 3 seconds, then let him go back to what he was doing. You don't want to cause over-the-top frustration as that will backfire. When singleton puppies are born, they often miss out on those lessons in building tolerance to mild frustration. A gentle rolling on the back for a tummy rub and affection is good too. It's associated NOT with punishment, but it may be a little uncomfortable for a moment. And yet, it's tied together with a taste of something good, a belly rub and affection. This conditions the pup to tolerate something that might otherwise cause a dog some serious defensiveness later on.
Rubbing toes a little bit, having him learn to get his nails clipped early on will help later. It should all be associated with yummy treats and a cheerful attitude...never undue force or tenseness/anger. Never. Same goes for other grooming; brushing, cleaning ears, teeth brushing. Started early, mildly, gradually, this pup will be able to tolerate these things nicely as he matures.
Socialization...getting him use to people coming and going, normal household noises as long as he's not over-whelmed or frightened is good. Be careful to back off on things if he shows fear and start with a more mild form of these things. Be careful about other dogs that you don't know for a while. When he's about 7,8 or 9 weeks old, other gentle, vaccinated pups who you know are healthy are good to get him around....all very controlled, not just random dogs. At the age of about 8 or 9 weeks, IMO, it's important to get him out and about, have people of various ages, sizes, shapes come over to visit, have him see various environments, objects and a whole lot more every day. But watch that you don't go where a lot of random dogs go. You do need to exercise reasonable care that he doesn't pick up some awful disease. Maybe just go to a friend's house or other place where a lot of dogs don't go. You can not over-socialize a dog IMO but you can over whelm him so a balance has to be found and frightening experiences must be prevented. After 2 series of puppy shots, I believe it's relatively safe to get him into a puppy class. If socialization is delayed or skimped on before they reach about 4 or 5 months, you will have one seriously messed up dog. Undersocialized puppies during this critical period (birth to 4-5 months old) are extremely difficult to fix. That window closes and it's too late. Socialization must begin as early as possible and continued diligently till he's 4-6 months old and continued forever but perhaps not in as saturating a way later on.
Positive reinforcement type training goes a long way in teaching a pup what he needs to know while keeping him happy and enjoying training. He learns how to learn better and the bond created is so much better than using a lot of force and punishment. (my opinion) But there are some things your folks can find out if they don't know already. A good training class, a few excellent books, some good links online can all be recommended here, plus help right here on this forum to give this pup a better than average chance of smooth sailing.
Anyhow, I'm sure there is a lot more that better trainers can advise or think of that I have not thought of. But I thought I'd toss in some more ideas just in case any of it might help.
