I am so sorry w.o.w. to hear of your troubles and your family’s.
I think you need someone to help, someone who can see things from outside and put them in perspective. But first of all, it is crucial to know more.
What is happening and why? I understand he is changing his lifestyle, but he is not even mechalel shabbat, not in public at least anyway. So what is going on? Perhaps the problem simply is that he would like to change his lifestyle (to some undetermined western teenager type, because he does not have anything that passionates him at this time? or does he?) and feels that the lifestyle he desires would be incompatible with observance. Then he needs someone who says that he does not ever have to do something he does not want to, including being mechalel shabbos, and who can give practical ideas and solutions. Is there something else, such as he does not believe in G-d? If so he needs to hear different things, such as that what he does is way more important than what he thinks. I think the most important point, and you should definitely have a rabbi he respects say this, is that – no matter what – he should never feel like a second-class jew. You can have the rabbi show up with some excuse, and if you think it’s better, he can say something like that about an imaginary person, rather than address him directly.
I believe it is very important that you protect your other children, not from his “bad influence” and stupid movies (which are available everytwhere nowadays), but from wrong ideas, such as this attitude being a good way to increase attention and love. Imagine in the future trying that with a spouse. Please, talk to someone who knows your family.