Everyone already said what i would say.
Your being there for them means more then words. It lets them know they arn't alone in their pain. And letting Keiana see it, in my view, is good. It lets her see the REAL side of life and death. And allows her to learn how to grieve also.
There are no magic words you can say to your brother, but being there for him is what's most important. And if you don't know what to say, tell him exactly that! That you are at a loss for words, but are feeling the loss WITH them.
I'm truely sorry for your familie's loss Kevin.