When I connect to my mac mini (from my Mac Book Air) what happens is that the connection is made as a regular screen sharing. So if someone connects a screen to the mac mini then all the activity is seen.
But if there's already another user connected then I get a message saying that another user is already using the display, and then I can choose to share the screen or to "login as yourself", and that's great!
How can I always connect as login so each user get his privacy?
MacMini: macOS Sierra 10.12.5
MacBook AIr: macOS Sierra 10.12.5
Using other software, RealVNC, should fix your problem.