I've been reluctant to post in this thread cos it hits too close to home for me.
I lost two of my brothers when we were 11, after they died I always felt like two thirds of me is no longer here, it's like someone chopped my right arm and left leg off, even now there isn't a day that goes by that I don't feel pain over their loss, for the longest time I existed but I didn't really live I was numb, the only thing that has truly brought me out to make me live again is my son I love him more than anything, though I still feel my brothers loss every day.
I think his reluctance to live has something to do with his siblings death, especially if he was close with them, extra specially if he was there at the time of their death - I was not. With my experiences with Psychiatrists and Psychologists in the past 2 years I'd suggest he could benefit from their treatment. It's not a feeling you ever stop feeling but I think it can be put in the right place.
Honestly if it wasn't for my son I would probably be doing the same as him right now, I think it's just a strategy to hide away from the world, before I found out my ex was pregnant my teachers also my parents wondered if I would pass grade 12, well I not only past but I got and OP 4.
Can I suggest you don't force anything on him no matter how much you think it might help, one of the mistakes my parents made when my brothers die was forcing me to talk to counsellors and all that when I wasn't ready, plant a seed during a conversation with him and see if anything comes of it.