Hey I have the similar issue like you.
I am dating with a guy who has a 14 years old son, we live together. We are not married yet but this kid is as messy as your son but he is a good kid.
I have tried to make him to study but he just keep playing vedio games all the time no matter it is weekend or week day. I have to do all the house work for him, cleaning. But I don't need to do a lot of cooking since he doesn't like chinese food that much. He only eat pizza and burgers. I tried to give him as much freedom as he needs but I found he has no control at all. Your article really teach me how to do for that kid in my case. I was kind of lazy to teach him things since he is not my son, I hate to take responsibility. I do everything because I love my boyfriend. You are a great mother, I should learn from you!!!