Hello! and welcome to the site! As for your requests I can help you with the disconect part, but it sounds like you may already be familiar. You have a couple options. The first being setting this up in Active Directory via the Terminal Services Configuration. The other would be to write a small script with the "Tsdiscon" command.
You should be running your backups after hours though when no one is present then when you disconect the session you wont have to worry about anyone logging on. The way I have it setup on our server is a scheduled task that point to the .bat file I created telling it to disconnect each session. I am sure there is some better commands out there.