Counesling. I was not as young as they are, but I lost my grandma on my 18th birthday and she was just about closer to me than a parent could be. And I lost my dad at 21. It's so confusing, I can remember being an "adult" and still being confused... and angry, I was angry at everyone. But most of all, I was angry at anyone who would say "I know how you feel", or something like that. I hated that. All I could think was "uh... no ya don't, you have no idea."
I think the most important two things are 1)was it sudden or had she been sick? I'm not trying to be nosey, but I experience both with two very close people in a short amount of time and I can guarantee you that having a chance to say goodbye and knowing what was happening before it happened was so much easier to accept. I don't remember having near the anger with that one. It was almost more of a relief by the time he went because I knew he wasn't suffering anymore. With the other, I didn't get to say goodbye, I didn't have a chance to get used to the idea... she was just gone in her sleep, completely unexpected. It took me a VERY long time to adjust to that one and I hated anyone in my path.
And 2) did they live with her? I don't mean to sound rude, but again, this mattered a lot to me. It's easier to do without something that you don't have every day, morning to night. While you still miss them just as much, your mind isn't dwelling on the fact that they passed.
I'm not asking for answers to these questions, they are just suggestions for you to consider when thinking about how to help your little brothers. Feel free to send me a message anytime if you need someone to just listen. Don't forget to take care of yourself... she was your mom too.