Sounds like an incompatible mod.
Are you using any ? If so, remove.
Sorry if this is an old thread, but I'm having the same problem. I've removed all mods and the issue still exists? It says they are both married and siblings and I don't know how to fix it. cas.fulleditmode has the dropdown box available but when I click to change their relationship it wouldn't let me click it.
Both have aged up in the same lot together, which I'm not sure if that affects things or not. One is a young adult and the other is an adult.
Try resetting your user files as described in the factory reset described in this post: http://answers.ea.com/t5/The-Sims-4/FAQ-Troubleshooting-Steps-amp-Known-Issues/m-p/3621199
You won't loose anything. Just make sure to not delete any files and make a backup.
After renaming, repair your game by right clicking on the game in Origin.
Try on a new game with nothing added back first (start new game). If it works, put back your save game and try again. If it still works, you can start putting stuff back.
The rest does not need putting back, cause they are mostly cache files that recreate or log files that are not needed for the game.
have you been able to solve this ?
