Basically, not sure how Apple does it though. You have a Google family group. You can add individual accounts to that. The group owner cannot see any activities of other accounts, but he could remove people without their permission.
Removed users only lose active family subscriptions like youtube premium and google one (storage). Their watch histories and whatnot will remain the same. Watch out with Google one. If you have Google one and use more storage than google free, then remove google one, you only get a limited time period to remove data over the limit. Afterwards it gets inaccessible, I don't think they delete anything, but no insurance on that.
I think there's SmartTube for smartTv's. Not sure how parental control stuff works.
Yeah, Nebula is great. But other than being not Google, their platform works in similar ways. You pay, you get content.. I mean, how could they even change that anyway?