Hey @blahbri ! Sorry you're having trouble. Take a deep breath. We'll try to help you get through this.
As @puzzlezaddict was saying, it sounds like you created two households in two different saves but I think you want both households in the same save. Hopefully, you haven't really lost anything except maybe some edits to the house of one of these famlies. When you create households, the game automatically saves them to your library. Open the game and load the save with one family. Then click on the lot where you want the other family. Click to create a new family using the button in the lower right of the manage worlds screen, then when you get to CAS, click on the Library button in the upper right corner. It's the button that kinda looks like a photo. If you're in online mode, you may need to click the tab labeled "your library". There you should see all the households and lots that you created as well as the ones that were pre-loaded in the game. Look for the other family you created and place them in this household. You'll be prompted to merge or replace, so click replace to load the family. Make any changes you want then click the check mark in the lower right. Now you should have both your families in one save and you'll be able to switch between them.
Edit: When you want to switch between households, you would click the Manage Worlds option instead of going out to the main menu.