Re: I Want My Sims In 1 World Together

@Pantherkat I assume you're talking about The Sims 4 on PC, so I moved you to that forum.

It sounds like you start a new game instead of making the new family in the same save file.

You can make new Sims to move in when you're at the world map. Just click on the play button when you start the game. 

Then you'll see this icon at the bottom right:

When you click that you can move new people in. You can also access the library/gallery and download other Sims made by you or by others to move in as well!
So if you have a Sim in another save, open that save, save the Sim you want to the library, open the other save and put the Sim in to that world.