I agree with greeteachday....I would explain that you can no longer subject yourself to him and his behavior, but that you love them and would like to see them, away from him. I would tell them that you have faced he needs to want to help himself, and if he does not want to do that, there is nothing anyone else can do.
I second going to a meeting, there is great support there, as well as here at SR. You are not alone!
Someone told me something once and I never forgot it. If you don't allow an addict a chance to face their own consequences, you are actually robbing them of any chance they may have of becoming clean. You may want to tell that one to your parents.
Glad you are here. Keep posting, we will walk this together!