If they aren't already using a password manager with an emergency access feature, get them set up with one. As an example, if you use Bitwarden then get a famil

If they aren't already using a password manager with an emergency access feature, get them set up with one. As an example, if you use Bitwarden then get a family plan and add them to it - that allows setting an emergency contact who can access or take over the account if needed. 1Password and other competitors should all also have this. The other thing you might do is have their banking and credit card accounts set up to email you transaction notifications - that's obviously more intrusive, but it should let you catch repeating suspicious transactions.