Lost CAS save even though I saved them to the library twice

Okay so I’m pretty new to the sims. I was trying to add another household to an already existing world, so basically I chose the save file I wanted, chose a vacant lot to move them into, and got started. It took me two-three hours to create two sims, and I saved them twice. But when I tried to move them into the household, there was an error and I lost them (luckily the og household is still fine.) I checked my files and I still have them, but for some reason the household just isn’t showing up in my library. Can someone give me some tips on how to get them back!? (Also how to better add another household to an already existing world bc this is stressful 😭🙏)