Please help me find this book?

I don't remember a ton about it, but here is what I do remember:

It's a teen fiction book. The apocalypse is supposedly coming and this kid's parents are "believers" of some cult who think that they can escape the apocalypse by going to the top of a mountain. The boy doesn't believe it but he has no choice but to go. When they get up there, he meets a girl who is in the same situation. But **** gets real on the mountain so basically a different type of apocalypse is happening up there. I remember that there were 2 authors on this book but I can't remember either of their names. If anyone could identify this book for me, I would be eternally grateful!