Syxarp Sorry for the late reply; I've been away from the forums for a few days.
What I mean is, open your save, go to Manage Worlds, click your household, evict the sims, and place them on a different lot, one that's blank or made by EA. (Don't use a Gallery build.) They'll keep their existing relationships within the save as well as almost all their other data, hopefully everything you care about.
If that works, you've left the problem behind on the old lot. If it doesn't work, empty their inventories; some items there (or simply too many) can also cause problems.