When I make a new household the rest delete themselves

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@jpkarlsen wrote:

You can only run one savegame at a time. It sounds to me like you think you can have two savegames merge into one. that is not possible.

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This is completely wrong. You can have as many savegames as you want. Don't confuse people by posting things that aren't true. OP never said anything about merging saves.

If you open any save, you can add as many households as you want to that save and then save it under a new name. You can then reload the old save (without the added) households, and play that if you wish. If you wish to move a family from one save to another you have to pick the family you want, export them to your library, then go into the save you want to play, and then import that same family from your library. And it's highly recommended to save it under a new name in case you change your mind (and so you can keep playing even if something goes wrong).

It is however NOT recommended to jump back and forth between multiple households in the same save, especially if you don't save it under a new name. Thanks to how buggy the game is, the risk of corrupting the save is increasing every time you jump to a different family. It's the same reason the game gets laggier and more unresponsive the longer you play the same line of succession of the same family. The game simply isn't good at handling a large accumulation of data, and that causes lag and save corruption.

That the save system is still broken after 8 months (and EA refuses to acknowledge it or do anything about it) is however a different matter, but the game is still made to support a new infinite amount of saves.