That basically does exist, and it’s called SSO. SSO providers (eg Okta) have a unified dashboard where you can control who can access what, and at what level, and can revoke access any time. It’d be nice if there was a version of that for families that wasn’t insanely expensive.
Anyways, 1Password completely solves this problem for me with me & my wife.
It doesn’t do anything for pushing authentication remotely or controlling access within apps, such as voice chat in Roblox. Each app has proprietary controls.
It also doesn’t begin to cover notifications. For some reason most services seem to think only one parent is in charge and both don’t need equal access and equal notice.