Sorry, I didn't check back.
Since it's only the one lot then it most likely that it's the lot itself that has become corrupt. It seems to happen with my Legacy families all the time as well, the longer you play them the buggier they get. Before you give up completely I have a few move out suggestions.
If you have Nightlife you can use the inventories of the families to take the most important items that you can't replace like career/aspiration rewards and the tombstones. (Honestly I do not know if the ghost will travel but it's worth a shot.) Maybe take their beds with you so they won't freak when you move into someplace new. (Also take any large items (paintings) that have appreciated so you will not lose the simoleon value and take large $$$ items that have decreased in value like the cars, hottubs etc, as well as things that you can't replace like pictures that were taken with the camera reward object) Heck take as much as your inventory can take.
If you do not have NL and "lose" your rewards you can use the boolprop testingcheatsenabled true debugger and shift click on the newspaper and get back your career rewards at least. Just turn it off when you are done by typing the command substituting true with false so you won't have errors popping up all the time on you.
If you really don't want to lose the house you can re-draw it on graph paper and then have that paper as a reference when you rebuild.
Also if you haven't downloaded the patch you may want to go ahead and do that as I think it corrcted the NPC slowdown bug which is what you lot may be suffering from as well.
You probably already know all of those things but thought in case you didn't I'd throw the info your way.
Good luck! I hope it feels a little better knowing that you aren't the only one that it has happened to.