Oh I hated this phase too. Grace is just now getting out of it. But it somes and goes still too.
Biting is NOT acceptable. Grab his snot and squeeze. I was taught that would discourage biting.
Maybe give people who are approaching him something to give him, like a bone, so he will associate people with treats. I tell everyone brave enough to meet my dog to get down on her level, hand outs palms up, and let her come to you...and NO FEAR.
Without being a complete tyrant, all of you will need to be assertive and authoritative. None of this, no stop that. Don't be afraid to take command. dogs pick up on our voice/tone and confidence level. If you sound confident but don't feel or look it, they will be extra protective of you. It's in the attitude.
Don't be afraid to find those pressure points on him and jab him. that spot at the base of his neck ... poke him there (with some force) when he starts getting snotty. That will get his attention.
But nothing will replace professional training and socialization. i know it's hard to socialize with a breed that no one will like no matter what. Unfortunately, you and me have 2 of those breeds. Grace would love to meet people, but she is a Rottwieler you know.
I make a point to meet "aggressive" breeds in the park. You can see it in the owners eyes as they get ready to pull their dogs away from people walking by. They almost cry when someone wants to see their baby because they've been shunned for so long because of the breed they have. I've met so many German Shepards and Pitbulls and other "scarey" dogs lately. They are all so sweet.
Good luck.