OK, I'm in the same situation ... except my wife hasn't updated to iOS7 yet. When she does, we'll have the same stations and history, I suppose.
Is there a way to turn off specific custom stations on each device? Right now, I have my iPhone, my MBA, and the aTV that can see iTunes radio, so it's not an issue as all stations were created by me.
As soon as my wife goes iOS7, then I'll get her stations as well.
Hope Apple figures a way around this ... or just let us delete/hide stations from individual devices.