Okay, I haven't seen the prior posts about conflicts between Tino and your son but lets talk about the lack of obedience. If you say you bring him to the trainers and he won't do anything but sit, and even that he has to be bribed with his tug toy, why are you giving the dog the option not to do his obedience? Correct the disobedience and stop putting him in situations where he feels he has to protect himself or his space. I don't care whether it is weak nerves or not, manage the situation and train him to do a behavior incompatible with growling and moving forward. In my opinion, being protective of you and sticking so close to you means a dog that is trying to manipulate you! You are not allowed to interact with men, says the dog. Did you think these men were a threat? Do you think people reaching into your van are a threat? If not, then tell the dog to move over and let the people in and if he doesn't, then feel free to correct him. Don't correct him for reading a situation, reacting and for you not liking that reaction. He's already proven that his reaction is not the right one, so from now on, stop giving him the option. Crate him and get rid of the retractable.

I am sorry to sound so harsh but I am jaded about people blaming the dog. He may very well have weak nerves, but he may also be reacting to your lack of leadership. Dogs will never hesitate to step into that role if no one is in it.