I think the article is about the sw passkeys, stored in a password manager. Not hw keys like Yubikey.
But your point is still valid. With passkeys the owner of an account would need to log in and add the passkeys of the other family members so they can log in. At the moment there's no way to share passkeys or even move them between password managers, I think.
But passkeys are still developing. I could imahine that in the future it would work like SSH keys. To allow someone to login to your account, you'd just add something like an SSH public key.
I find passkeys very convenient, but it's going to take a long time until they're supported widely enough for regular people to care.
There aren't that many providers who have gmail-like labelling functionality, but luckily Gmail serves labels as folders over IMAP. May cause a lot of duplicates, though.