Gnome is my choice because it doesn’t look and feel like it was designed in 2015. I also much prefer the workflow with the touchpad gestures. I used to have extensions but since I reset my PC and didn’t install any apart from the one that shows my cpu temperature in the top bar.
One way would be to let them find out the hard way. Make sure they understand that everyone can see what they do and say and that they can find them back as a first base step. Let them have to click the right download button when downloading a mod for their game, you know. Make a setup so that if there’s theres a big oopsie with their devices yours arent affected. And from there they will install an ad blocker or learn to find the download button. You could also make a fake blackmail or phishing email to see how they react (I’ve thought about making a fake phishing email for the elder ones in my family recently too…) and make it so that if they click, the screen goes black and red with crazy sounds.