remote access via LAN over internet

I have a group of 5 PC's all win10 connected together via a private LAN. These are all remote from me. One of these has wifi and unattended access teamviewer loaded on and is working great, I can access the public shared folder on each of the others. But how do I obtain unattended access on these . they have no internet connection. (Someone at the location can help but is a computer novice ) I can get treamviewer loaded on but I'm told it shows 'no internet' and fails to start the program. What is the best route ? VPN maybe?