Holy Cow I am in the EXACT same boat almost.
I have an 11 year old baby brother who is extremely lazy, has a lot of anger issues and many, many other issues that I feel need to be dealt with professionally. Actually... one of the first questions I ever posted on this site was about him because he had wiped his feces all over our couch when they visited us... not once but 3 separate occasions. If you look into my profile you'll see where I posted it... but thats just an example.
My mom won't hear it either. Our dad died in 2006 and I think many of his issues are directly related to the fact that he never received ongoing, long term professional therapy - and neither did my mother. But ...none of the details matter.
My mom won't listen at all - gets angry and defensive.
My own counselor has told me that in situations like this, its best to get off a sinking ship. I have no legal rights, I have no say in what she does as a mother or what he does as a minor unless its illegal... sooooo, yeah.
Its really awful, but I've had to let it go. There isn't anything I can do, and I sure hope you get some more advice and answers, but from my perspective, there doesn't seem to be much you can do : (
Hang in there... hopefully you'll get more answers over the next few hours!