I'm on laptop, in that window. I click + symbol and and navigate to the computers and hard drive in other room but they remain greyed out. The add button greyed out, no matter what I try.
If I understand you correctly, you are on the wrong computer. The setup in the screenshot I sent would be on your desktop computer
. On the laptop open Finder, then under Locations
in the sidebar, select your Desktop computer, then either select the shared volume on the desktop computer to open it or click on the option to share the desktop's screen. (You may have to enter the password for your account on the desktop machine. )