New Ideas

I've been considering some ideas and discussing them with a friend, and have come up with a rough outline of a story.
The setting will be post-apocalyptic/post-disaster. The story will follow two seperate groups, each consisting of two closely related friends/relatives. The two groups will follow seperate paths until they meet. One group could be two brothers, and the other could be two sisters. I have ideas for what will happen when they do meet which will allow for a lot of emotion (due to to the characters from each group being very close to one another).
I am considering the cause of the disaster, and it may be due to a nuclear bomb. This will be hard to set the scene for however so it may be for another reason, perhaps on a smaller scale.
That's the very brief outline of what i'm considering so far.