Remove sibling relationship

@laheehamzi1221 That's an odd issue. Do you have OneDrive syncing your Documents folder? It has a tendency to revert changes made in Sims.

Could u tell me more how can i find that? And could u tell me what if its not problem what should i do..?

OneDrive is a software program that syncs your Documents files with storage on the internet. You'll find it listed in your apps. There's a lot more information on it here, including how to get your Sims files out of it: https://answers.ea.com/t5/Technical-Issues-PC/CURRENT-ISSUE-Sims-4-saves-user-content-disappearing-PC/td-p/12475370

There was no onedrive..

At some point, the siblings relationship was added to the couple sims .( I will call the man of this couple ‘D’ and call the woman of this couple ‘L’) I guess this error occurred cus I added L to D’s family and delete L’s family relationship with D’s other family a few times.Even if I deleted the sibling relationship using mccc, the sibling relationship is added again after editing sim or managing the village.(I was really noob so I didnt know how to solve error.)So I clicked the new game button after saving the couple in the library. And Its been 2month that I started new game. But I miss the other family(D’s parents and siblings.).but I deleted D’s parents and sinlings in library since If i add D’s parents and siblings to the game and make them to be a family with D , the sibling error occurs again.Im thinking of recovering D’s parents and siblings . So I’m going to copy old save files and put them in the save folder after deleting my current existing save files, then save only that family in the library and delete the old save file again and fill save folder with my current save file. Is this a safe way ? If I do that , Can the sibling error occur again?

@laheehamzi1221 The only way the game itself could turn two Sims into siblings is if during the changes you make, you make them both children of the same Sim. And nothing the game itself does can revert to an earlier version of the relationship; that can happen only because of changes you make to households.

Nothing you do in the Library affects saves. The only way Library Sims end up in your game is if you put them there or if you use a mod that does that.

I suggest this, as both effective and giving you peace of mind:

1. Move one Sim out into their own household
2. Save each household to your Library as a separate, single-Sim household.
3. Select "New"
4. Load the two single-Sim households into your game. They will have no relationship to each other
5. Merge the households through the Manage Households menu
6. In CAS, make them married.