Years ago, it was just called Google Apps and was for bringing your own domain. It was even advertised as something that would be good for family usage. And in the legacy GSuite migration debacle a couple years back, they acknowledged that there are legacy users that were/are using it for families and that it would continue to be free (after months of uncertainty).

I have considered paying for YouTube Premium for the family, but I can't unless I create dual identities for all my family members and have them use both accounts on all their devices.

It is NOW, not when many of us created these accounts ages ago. (We were paying customers back then too!) Back then, you paid Google to use your own domain and to unsubscribe to data collection, I think.