Actual, Jordan having special needs probably does have a lot to do with this. I'm assuming he acts differently than most other people, maybe not by a lot, but with as perceptive as dogs are with body language and what they're socialized with as "normal", a little can turn into a lot.
Not all dogs like to be hugged...it's a totally foreign concept to them. Keanu growls to let Jordan know to stop it, since Jordan doesn't pick up on the lesser signals. Neither does Jordan acknowledge the growl and stop hugging, so Keanu feels forced to go to the next level, which in this case is mouthing. That's actually awesome, that he's still using that much control, especially since it looks like Keanu is pretty young himself.
Anyway, I'm assuming that when Keanu mouths Jordan, Jordan stops hugging him and goes away? Keanu just got the result he was after and that is the reward. Since it works so well with Jordan, he's going to try it out on everyone else to see who lets him get away with it. I'm betting you and Johnny don't, so he's not going to try it with you.
You need to get it across to Jordan that he can't just come up and hug Keanu, he doesn't like it and he's being very polite in saying so. I imagine Jordan is hugging because he knows it's a nice thing to do to someone you love, but it's not going to work in this case.
I would say to tell the rest of your family to ignore the mouthing but I don't know those circumstances well enough to feel comfortable saying so. Growling is a dog's way of communicating his dislike and if we don't "get" that, he will escalate to something we do understand. But you shouldn't let him turn into a pushy little brat either...there's a line there, but I can't see it over the Internet.