I think I've found the reason why error 533 is happening, and a working solution (as of now).
My sister has been receiving the 533 error while trying to save. She has been playing on the same save for quite a while, leading to quite a few households dying off with only one ghost remaining. These single ghosts are living in houses, but do not appear to actually be registered in the game as households in household manager. I went ahead and deleted all of the ghost "households" by evicting them from their houses, which placed them in the household manager. That seemed to fix the issue for now!
If you don't want to delete the ghosts for whatever reason, I suggest trying to re-create a household for them.
If the 533 error comes back, I'll edit this post to let you all know. Hopefully this helps, and if it works for you please let me know! 🙂