That definitely sounds like a good way to go. He breaks it every day, so it would probably be the first thing I'd do every day when I get to the house. I'm wondering if there's a way to make it restore itself every time it restarts. It sounds like this application isn't made for something like that.The reason I stressed an external hard drive was to remove any chance that your bro could get to the stored snapshots
Restoring is like toasting a slice of bread..Simplicity itself.
Even if he manages to screw up your abaility to boot the pc he uses......you can boot that pc from a usb stick with Linux mint on it...access Timeshift .....it will "see" where the snapshots are stored (have the external plugged in)....hit Restore....and away you go again.
My brother's situation is a very uncommon one so I don't expect a terribly simple solution to it, but maybe if I could figure out how to make it automatically boot up from a backup it might work