Users visibility to admin and able, not able to initiative conversation

Hello guys, I have been trying to find out how to do it but seems nothing so far, so my question is:

USER A simple user

USER B simple user

USER M power or admin user, or simple user

I want the USER M behing able to see and see and initiate a conversation with USER A and B, and the last two can reply, but i don’t want User A and B being able see and initiate a conversation with USER M.

Is this possible to do server side ? or any other way ?

Thanks in advance

Sorry to insist people.

Anyone could help me on this?

Thanks