Granting server access should have an option to allow all managed users in the sharee's account

I want to share with my two friends. They both have managed accounts for their wife and child respectively.
This now means I need to share with 6 different accounts respectively as opposed to 2.

However the main difficulty is that now, they, wanting to switch between a parent and a child or a spouse and a spouse, now need to go through the tedium of logging in, typing in the password on a remote, performing MFA etc. The friction is not viable for a paid product in 2025 when I should be able to devolve sharing to all managed accounts in an account I grant access.

Switching to a different user within a Plex Home definitely doesn’t require a completely new login.
If they have created full plex.tv user accounts for each family member, they can invite them into the same Plex Home, thus enabling Fast User Switching.
Inviting full plex accounts into a Plex Home is a Plex Pass feature.

As for the first part of your request: there is already an existing feature request for it. Allow managed users to have access to shared content