Culling in the Sims 4 for Sims Living in Houses

I have created families, and when I saved them, they would disappear with each new family. I was on the PS4, and I couldn't understand why.
I figured out that in order to keep all your families in the game, you have to save over the previous family. It keeps all of your Sims, and you don't lose them, all you have to do is keep track of each save file in order not to save over another one.
Also, make sure to play the families you want to keep, so the game doesn't cull them.