@Helene12345 You can save all the sims to your library, as has been mentioned. While, as you have experienced, this will delete all their relationships. In the edit households, you can download the family from the library in the CAS, set their relationships and then move the extra's out to their own household. You can do this for each sim that is related by simply adding them to the household from the library while in the CAS. Adding them to a household in the CAS from the library is the only time you can set their relationships without cheats.
The only way to move the sims and households is through the library to new saves.
For saving apartments, you must delete the walls where the doors are to make the apartment one large room. You can then save it to the library as a room and transfer it to a new game.
Also, you posted in the correct section, as your issue is general game play and not at all a console tech question, which is what the console board is.