My Nephew Is 17 And Should Be A Senior In

My nephew is 17 and should be a senior in high school this year. However, he has not been to school for over 2 years and has not followed through with the "at home" program he is supposed to be following. His parents tell me that he wouldn't talk to his therapist so he is now just going to his GP. He has been prescribed medication but isn't consistent with taking it. He stays indoors and plays video games and watches tv all day and night. On occasion he does things with a youth group (like a summer camp at the beach) or his family (movie, out to eat etc.). His 21 year old brother is his closest companion. I feel like the school system, doctors and his parents have let this go on too long. What would you suggest? Obviously, he is very depressed.