i cannot begin to tell you how worried and angry i am

How do you convince a young, disoriented boy with a fundamentally twisted view of things that what he is doing is wrong?
How do you explain to him basic rules and facts, when he doesn't want to understand, but rather to stay ignorant because it's easier?
How do you tell a sixteen-year-old child that if he continues to do what he's doing, he will fall, and his fall will hurt, and it will be permanent?

My brother is, indeed, a child. He wishes it were different. In fact, he is convinced that he's all grown up already, but that just isn't the case. There is so much to learn and understand before he can call himself an adult. Things like wisdom, and responsibility.

He's intelligent, I'll grant you that. He knows things, he sees things, he understands things. But what good is intelligence when he doesn't make use of it? He stashes it away, he kills it off and lets it go to waste. I've heard what goes through his head sometimes. There is an old heart in that body, and it's good, serious heart. Why does he choose to stifle it?

He doesn't have a shred of responsibility. He swears and promises and never goes through with what he says. He doesn't work. He doesn't even try to keep up with schedules or any rules, as a mater of fact. But even though he screws up continuously he still keeps lying to himself and others by swearing and promising again, and again, and again. Make no mistake, my mother is also a fool for trusting him every time and then being continuously disappointed.

The problem is that he has very twisted priorities. While he's still a minor and has an obligatory amount of education to go through, he's still somewhat out of harm's way. But what will happen when he'll have to stand on his own two feet and fend for himself? How will he learn how to lead an adult life? And when? My mother can't just care for him until she dies of exhaustion.
This boy isn't even capable of cooking a meal other than ready-made food. If things were to go his way, he'd live on yoghurt and ravioli. He'd get sick, he'd drown in garbage because he can't even bring himself to throw things away properly, they just lie around until someone throws them away for him because it's unbearable to watch. He can't operate a washing machine, he doesn't know how to handle money wisely. He's already in debt for a few hundred with his friends. "Friends". He's sixteen and already a few hundred in debt. Just let that sink in. How is that even done?
He does nothing at school. And I mean literally nothing. He doesn't listen, he doesn't do his homework, he doesn't care when he's told off, he doesn't react to scolding. He just doesn't care. He doesn't give a single flying fuck. My mother is spending thousands of francs on private schools because public schools won't have him any more, but he just doesn't give a damn. What is it to him that his mother, our mother, is working her ass off to ensure that he gets a proper education? What is it to him that she is so exhausted that she's aged drastically in the past two years? It's killing her. He's killing her. And he just doesn't care.

How do you get a teenager to care? How do you get him to understand? How do you get him to understand that all actions have consequences, and that his actions are very, very harmful, both to him and his surroundings? How? How?