Your daughter also needs to be firm and issue a voice command of 'No' when the dog nips you - she is the owner and needs to be responsible for teaching it that this behaviour is not allowed. And she needs to be consistent.
As already advised, you need to completely ignore the dog whilst your daughter/ Son in law say No and call the dog away. When the dog is under control again, have a treat and call him to you and make him sit. Give him the treat and give him a fuss and if he goes for you, the daughter/ Son must repeat the process immediately ('No', call away, whilst you ignore).
The puppy is looking for a response from you and so far it is getting a reaction. If you give absolutely no reaction to his bad behaviour, whilst the owners distract him and and let him know that he is not allowed to bite, he will eventually stop. Then, when you call him to you, to sit - he will eventually get to know that when you enter the room - the only way he will get a reaction and a treat, is if he sits nicely and doesn't bite.
Good luck, persevere, and be consistent with the training and it will work.