Hmm, the same family could be neat... but I like the idea of having two different families as well. 

Lets go with your original idea and have them live in the same neighborhood, how does that sound? The families can be really close and we could even set the RP in the summertime so that they could get together a lot for the kids to play and the adults to hang out? That way it won't be us RPing with ourselves too much.