Keeping the family tree?

I imagine most of the families in your world would be related in some way by the 5th generation so I think the best way to move everyone to a fresh town would be to use Nraas Porter. There's a tutorial at the Nraas site on how to use Porter. It's quite easy to use but there will be some reshuffling of sims when they are unpacked in the new world. I have found most families are kept intact but the odd sim gets separated.