Sims 3 Folders

@Regi67  I don't know anything about either of those games, but I can ask around.  Installing the games themselves shouldn't have had any effect on TS3, and you have more than enough drive space to accommodate them.  The only thing I can think of is that perhaps you or your son updated your OS or installed some other software to make the games run more efficiently.  Windows 10 runs TS3 just fine most of the time, but it has been known to get cranky.  (And the multiple TS3 game folders suggest an update—OneDrive likes to reenable itself without asking permission.)  As for any other software, I'd only be guessing.

I still think that the issues are more likely due to some corruption in your ongoing save.  The other games wouldn't touch your save files, and since a new save loads just fine, the problem is probably the save itself.  What you've described is how game corruption can look, at least once it's progressed past a certain point.  This is one reason it's a good idea to keep a few backups of your current game.  You can use "save as" and rename the save; I do so at least once every sim-day, and I keep 4-6 older saves at a time.

By the way, you may not have to recreate your sims.  Any household you've created will be saved in a file in your game folder (your old folder, in this case: the path is Documents\EA\TS3\Library).  The names of those files are random, but if put them into your new folder, they'll show up in the bin when you select a household to move in.  The same goes for any builds you happened to save to your library.  You can also save an individual sim to the in Create-a-Household and then reload that sim later to work on or add to another family in progress.  Those sims saved in CAH have corresponding files in your game folder, in SavedSims.