Pernille, I've had that issue and have managed to sort of fix it, but I don't recommend trying this without challenge board approval. When it happened to me it was a regular file, not a challenge file.
What I did was move the family out to an empty lot and save them to the library. Then I saved a copy of the now-empty house to the library. I then bulldozed the house, so it was an empty residential lot. I also bulldozed the family, removing them from town. Then I placed the copy of the house on the lot and the copy of the family in the house. If everything worked out properly the family still had all of their things, relationships, jobs, etc.
To be honest I had this happen frequently in an older patch/expansion version of the game, and it generally came from travel and it generally meant the game was already a little corrupted. There were times where I could fix the file, and times where the fix was temporary and the issues slowly started happening again. Hopefully what you're experiencing isn't this and you're able to fix your dynasty and carry on. Best of luck!
Thank you for taking the time to make a reply! if I don't find any other way I might try this and just play an unofficial dynasty.
My favorite Sims 3 help blog says to change active families and move the family back in and out.
What worked for me last time was splitting the household sending the affected Sims to another household. Then asking them to move back in.
I've also had this issue with certain outfits too where I just had to have the Sim change outfits to come back but if you can make them do this I would try the split household. Is it one of your heirs/immortals that are affected?
It is my founder and the spouse of generation 3 who are affected in the latest save. The thing that really baffles me is that in saves that I have previously played without problems (meaning I have loaded from that save before without issues), my founder also is unresponsive as well as sims that I haven't had any problems with at the time I played the save (ex. generation 2s spouse). I have no idea how that is possible.
I cannot select them at all, so I'll go on and try and split the household and see if that works.
Thank you for the advice:)
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ETA:
My founder has travelled but that was when gen 2 was YA and she hasn't travelled since. Gen 3's spouse hasn't travelled at all. I have used the relationship changer heavily (though not to change relationships between the founder and gen 3) so I don't know if that has made them appear twice in any relationship panels and therefore made the game file break. I cannot select them so I can't see their relationship panels.
I tried changing active families: no difference
Move them out and back in edit town: no difference
Send them out using the move out option: they disappeared but I could not use buy mode since the game thought the moving still was in progress even a sim day after they moved out = didn't work
Split the households in edit town and made the affected sims merge with Martin Grundgrabses family. Their portraits are still missing from the relationship panels. Befriended Martin and tried to make household visit. When the household screen came up no sims were present and I therefor couldn't invite them. I didn't see the sims either when I visited the household = didn't work.
Am I allowed to try and make a copy of the family and the house to the sim bin, delete the bugged house and then replace it as Vinyl suggested?
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ETA 2:
I tried Vinyl's suggestion and it worked, but now all the portraits were missing. The photographs and sculptures were intact but the most important part, portraits, were missing. Typical.