I once managed to make it work with a computer from a different country and with a different party plugin we used 2-3 years ago, SimpleFollow. No experience with AutoFollow here but it seems similar, take this hits with a grain of salt, but this is the way I would start: First try to make 1 server and 1 client working, both different computers. This is the hardest part.
1. AutoFollow settings, Bind Adress: server_address on clients, can be localhost on the server or the same IP as clients have
2. How to get your local network server's IP? Run cmd on the server comp, type ipconfig /all, find IPv4 Address, for most of the routers it's 192.168.1.X. This is your server's IP in the local network, it can be changed daily, weekly or never at all, depending on your router's settings. Ideally you would like to have fixed IP settings for your server's computer, most of the routers can do that. Also this is the IP all your AutoFollow clients should have in their AutoFollow settings. This is also the IP you can fill into server's settings, or keep there localhost, it should not matter. Port can be kept as well on 10920.
3. In theory now your clients should communicate with the server. Another hard step is to allow this communication to pass all the blocking layers your Windows and router may have set in place. Unpriviledged communication port 10920 may be blocked in the router and will be definitely blocked by Windows firewall and by default will be probably blocked by any kind of defender or anti-spy/virus software you are running under the Windows.
I would also go through the AutoFollow thread in Plugins, I vaguely remember seeing this topic somewhere. Be patient while searching.