Some people are so overly paranoid lol. Like anyone is going to put in the enormous effort to get the data off some random persons HDD.

If they/you can afford it, something like a Firewalla would work well. I would also look into changing the DNS like others said. Perhaps a simple raspberry pi with pi hole on it.

Also thank you for helping these people out. It is hard for them to know what is going on when they weren’t brought up with it. It is even harder to train them to do something different from what they have been doing for so long at that age. I hope you find something that works for each of their cases.