Teenage boy alt right radicalization. Help Resources?

A friend of mine is mom of a few teens. She’s becoming increasingly concerned about the mental health of her 16yr old boy. He’s becoming erratic and aggressive, alienating his other siblings as well as her. He refuses to continue to speak to his therapist. She is trying to get him evaluated by a psychologist. Meanwhile She is beginning to suspect by the things he says in his outbursts that his time online is being spent in far right wing circles. We went down the Google rabbit hole about possible therapy options specifically targeted at deradicalization of this kind. But found it all a bit overwhelming. Does anyone know any resources or have personal experience with this sort of thing? A male friend of mine a few years ago died by suicide but before this occurred he went down a dark path of online ideology after college that seemed so different from the person I’d known him to be. The things my mom friend is witnessing with her son makes me worry for them.