Odd Apocalypse question

I am looking for a book I read awhile back. It's an apocalypse book. I don't remember any zombies so must have been something else that caused it.
I remember there being two brothers. One good. One bad. A woman, who's mother left her ages ago. A group of them find a secure place outside of Las Vegas. They have to eventually go in to the town for supplies. Lots of bad guys in the casinos. The woman finds her mother in Las Vegas. Not happy about that. The women get kidnapped at one point and have to be rescued.
The bad brother ends up with the woman's mother, which she hates. The bad brother eventually comes around to being helpful.
I'm pretty sure it was a series.

Sound familiar to anyone?