Yes, T.H.E.R.A.P.Y. I don't think you can do this all by yourselves. These aren't just "Behaviours", they're more ingrained experiences and emotions he's acting on, with an unfortunate limitation posed by his ADHD (if that is the accurate diagnosis).
Although I agree about family rules...every family needs those...I think you need to do some preliminary work not so much on the "Rules" side of it, but the "Family" side of it. Have you all ever sat down...even over dinner...and just talk about your little family? Do you do corny yet highly effective things like have "Game night" where you play board games? How about going out to dinner? You know, things that foster emotional bonding. Do you guys kick a soccer ball around or go look at cars together?
I think this kid is struggling with a lot of very difficult issues...look at how torn up you are as an adult, imagine the effect it has on him. before you can expect him to accept the rules of your family, you have to make sure he buys into your family int he first place.