what can we do to futureproof our relatives?
Most of the phishing I usually get is about things I don't have. But just one week ago I've received one that looked very convincing and almost got me... but my usual way to handle this stuff saved me and.. at least for phishing I do have an advice: don't ever click the links from e-mails, go instead directly to the related app or website and check there, usually you should have a message, warning, whatever. Else.. it was probably phishing.
For the cases they may e-mail (or phone!) the parents that you're in trouble... it's more difficult, indeed. The only idea I have is something I've heard of for keeping the smaller kids safe: discuss about a number, phrase, keyword, whatever: only if that is part of the e-mail or discussion it will be taken serious, else it can be considered fraud attempt. But, I know, this doesn't apply to all possible cases.
At least in case of arrest a phone call is permitted, right?