Sims 4 overwriting

Are you trying to play on the same computer with the same user? The game code can only be accepted once by the EA authentication system. After that, the code is locked to that Origin account that was in use at that time. The game saves game data to the user document folder who is logged on to the computer. If the other person logs on as a different user then the save data will be saves to that users documents folder and shouldn't over write the other user saves. If you are using the same computer login you could use the "save as" option and load the appropriate save when the next person plays. Only one person can be logged into an Origin account at a time. 

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