I really don't know what to say, except time will help all of you get through this terrible situation. Come back here and tell us how you're feeling as events unfold. Talking helps, even when it's difficult.
Kids are pretty resiliant. Be a good listener for them.
I'm sure you'll do fine at the service. It's good of you to be there to help those he left behind.
Hang in there.
Cheers,
Scott.