What we did to protect my MIL from "next time"
I inspected her computer and found five different remote access programs that were installed. I removed them and removed a suspect program that had no purpose being there. We reviewed her accounts to see if there was other strange activity. Then, taking it a step further:
Replaced her Windows Home with Windows Pro. Windows Home has limited ability to lock itself down. Thanks Microsoft.
Set up a user account for her with only necessary functionality. Set it up to disable installation of new software, which means no more "remote" software.
Created a cheat card that is taped to the laptop. It has a short list of what to do with any call, text or email. Essentially: Hang up or ignore.
Moved her to a new email account and discontinued the old one. She was getting hundreds of emails daily, scam, spam you name it.
We review her various accounts about once a week. Thankfully she gave my wife permission to do that.
Sat through a couple of the shorter Kitboga youtube videos with her just to try to embed a little distrust and maybe give her some understanding of how things happened. She said she felt better after watching because some of the experience was just like what she could recall.
At some point, maybe a year or so, we will need to take control of her accounts/bills etc. because she won't be able to fend off the scammers or remember to pay bills etc. It sounds to me like your father-in-law is already to that point. Best of luck to you.