I agree. The dog is the one running the household, and unless your parents want to take control, things are not going to get any better.
I would immediately stop feeding him people food until he learns some manners, if even then. I agree to start him on NILF (nothing in life is free.......... he must perform a trick/command before he gets or does anything, including eating/going outside,playing,getting a treat,etc)
If you can get your parents to take him to an obedience class it may help not only the dog, but them understand how things must work. Sometimes people have to be shown how to do things before they will change.
If they do not want to work with him or help in any way, and it appears you cannot take him b/c of your living situation..... ........please consider a rescue or re-homing instead of putting him to sleep. Especially if it is just a behavior issue and not actual aggression (you would probably want to talk to a behaviorist to make sure.......but it sounds like a behavior issue to me)