Or maybe just like the Bitcoin offline signing. The people who are managing the account can create a note that could be send to the owner of the public key, the owner sign it and either send to to relay or send it to maintainer so he can send it to the relay.

Yeah... that's it ... a platform where the owner of the npub can receive propositions of the people who manage the npub and with extension of the browser he can tick in or tick out the notes then sign and publish a note.