Hi "Bubba"-master!

First of all i want to say how much i admire people who help pets with a bad/uncertain/problematic/tragic history. It is so important to take care for them!!!
I understand that it gets problematic when your parents start to worry about Bubba. But you have to see that he has been with you and your surrounding just for couple of days. He must get used to his new family and i can imagine that he is a bit confused about the new situation, so many people around, another dog, you who took him out of the kennel, sudddenly inside the house where he cannot follow you ....
What i find very important is to show him that you and your parents are the ones who take care, who deal with people, other dogs, "problematic" situations from the very beginning. Start working with Bubba on a daily basis. Work on commands like "come", "sit", "stay" aso and praise him whenever he did well, give him treats immediately after he did well. But make also sure that he cannot follow you everywhere you go, he is not your bodyguard and he must understand and accept that. Also when you are at home a lot, let's say on a weekend, do not let him follow you all day long. Make him stay somewhere, give him something to play with, etc.
Make also sure that he can drain his energy when you walk him. Give him the chance to run, to feel his power and to get a bit tired afterwards, that is very important!
Walking him on the leash is also an important point for your relationship. Whenever you walk him, take him on the leash and have him walk by your side. He should not walk in front of you or anywhere behind you. You decide where to go, how fast you walk, and he must be by your side. By training this he gets the security that you are his master (in the best sense of the word!) and that he can trust you and must not care for "human" things.
Whenever you sense fear in him, ignore it and get him out of the situation as calmly as possible. Whenever you get excited, Bubba will as well.
One more thing concerning this training: if your parents could do that as well, it would be good, because in this way Bubba can accept them as his masters as well.
So, i think that's it for the moment. If you have any further questions don't hesitate asking, i would be happy if i could help.
In the meantime: all the best for you, your parents and Bubba.