found : to have the game regenerated the premade familes in house bin : delete or remove the lot catalog folder from your my documents/ea games/the sims2 and load the game. The folder will regenerate with the inoccupied houses and the occupied ones complete with their familes.
Good work - it's a very useful thing to know, and I can see it applying to other things too.
Hmmm. I need to investigate further.