I agree with what's been said. It sounds like he's really bonded with you, and it just sounds like he's showing his affection and potentially trying to "herd" you with his mouth. I'd tell him something like "OW!" very suddenly so he breaks his focus, and then switch it out for a toy, and when he takes that instead, praise like crazy.
As for getting him to pay attention to other members of your family, it's important for them to keep your puppy as engaged as possible while they're trying to maintain his attention and focus...i.e. high value treats (cheese, turkey, ham...mine loves cheerios!) and make a game of it! I've found that when I'm training with my GSD, a single treat per trick/command doesn't really cut it. I figured out that if he does something good, even if in the beginning it was simple, I'd give him 4 or 5 high value treats one after the other, and really try to engage him, and run around and keep his focus and attention by making training into a fun game for him, instead of a static exercise.
It sounds like you have a lovely dog, and a companion for life, it really is just a matter of being as consistent as possible with training, and not letting your blood boil when they're being a brat