Holly crap...
I'm truly sorry for your loss. It sounded completely unexpected. I'm not good at this sort of thing, but I will say you and your family will be in my prayers and to try to keep your chin up. You don't want to hear this is part of life, but know that he'd want you to remember him and move on. I'd just try to focus on being there for your little bro' and your mom and be the "man". No one should have to do that at your age, but I'm sure you can find the strength. Make sure you take time to grieve, too, but try to be there for your family, too. This is going to be a tough time for all of you.
Hang in there, man
Respectfully...