Rather than sending an article that they'll ignore, I recommend helping them do it when you visit. Note: you're guarding against phishing and also locking themselves out of their accounts. Both are important.
I bought Mom a Yubikey and helped her set it up on her Google account. She has it on her keychain. She doesn't need to remember how to use it, though, since it's only needed when she buys a new computer.
For good measure, I also helped her print out backup codes (and I know where they are) and I registered my Yubikey, just in case.
Nowadays, an old backup phone might also work, but I think paper backups are better because an old, unused phone might not start.
I bought Mom a Yubikey and helped her set it up on her Google account. She has it on her keychain. She doesn't need to remember how to use it, though, since it's only needed when she buys a new computer.
For good measure, I also helped her print out backup codes (and I know where they are) and I registered my Yubikey, just in case.
Nowadays, an old backup phone might also work, but I think paper backups are better because an old, unused phone might not start.