Some of you probably have moved sims to the bin to place them in a new town only to find out those sims have lost their family tree. Normally a dead sim will still be count as a family member, but once moved their gone.
You can prevent that by taking the tombstones of the past away sims on your lot before backing up that lot with family to the bin. That way your game will still see them as family, and they will come out at night to hount your yard.
If you want to have only the family and not the house they are living in, than be sure that all the tombstones are in the family inventory.