I have read this these generic instructions to log users out, but I want more detail.

When I run the command users I see multiple instances of the same user. IE:
Joe Joe Joe Joe Joe

How do I know if Joe is active? How would I find more information about what Joe is doing in each session? (like can I close a session Joe has open, and not loose his work?)

I am familiar with the w command. Say this user left his terminal on at home, then came into work; but rebooting the server isn't a good idea, I just used the command

pkill -KILL -u Joe bash 

This threw me out of the shell and out of the open-shell from home, with no idea if I'm loosing work in this process.

What can be done to help me evaluate which sessions can be closed safely?

I tried

skill -KILL -v /dev/pts/1 

to kill a specific session, but nothing happened.