This is a puppy. Whatever type of training you are doing may not be the best for this pup. Are these bites that are breaking the skin and needing stitches, or is the dog seriously mouthy? The reason I ask this is that I have a puppy that has been gone for five months and is now back. She is fifteen months old. And she is mouthing my hands like crazy -- no blood -- this is NOT aggression. But if this was my first dog, I might think it was.
So, before we euthanize this pup, it would be good to know what is going on with the bites themselves. Are they breaking the skin, is there bruising, is the hair up when this happens, is there snarls, growls, show of teeth before, are the lips drawn back or forward during? I am guessing it happens fast, but it can mean two different things.
1. If the pup has something physical, thyroid, b-vitamin, not sure what all, that can be diagnosed and treated with meds/vitamins, that is the first thing.
2. If this is a fear/response, than alpha training is not going to help a lot. MOST bites do have more to do with being unsocialized, fearful in the situation, than dominant aggression. If he is fearful, continue NILIF, and continue to train him, but set him up to succeed and praise him for it, build his confidence and build his socialization experience, muzzled if necessary, not to the point of people touching him, but him in a variety of situations where he is not hurt. Try to keep it positive.
3. If this is a dominant/aggressive situation, I wonder if you are right for this pup. Sad because unless you find the right person with full disclosure to take him and work with him, your options are really limited.
Remember thought that this is a youngster. If three people have headed off to the ER already, well, I think you need to maybe think about taking him to the vet, and doing what needs to be done, sadly. But if these are inhibited bites out of something that might be worked on, well maybe he has a chance.
Good luck with the puppy. We do not know what happened to him before you got him, but that is over and done with, you cannot change it, and he is living in the moment. He probably was not socialized, which makes your job harder, but do not give him the you-poor-thing treatment because of what MIGHT have been his previous situation. At the same time, if you are alpha rolling this puppy, you might end up in the ER.