Make sure that you and your friends are using the same version of the game (Steam or Goldberg Emulator) and mods. Steam Overlay should work.
Create Co-op Game
Step 1: Install Radmin VPN and create a network Download and install
Radmin VPN. In the main Radmin VPN window, click "Create Network".
Enter the network name, password and click "Create".
Step 2: Ask your friends to join the network Send your friends the name of the Radmin VPN network and the password to join to this network.
Step 3: Install Painted Worlds Download and install Dark Souls 3
Painted Worlds.
Step 4: Install Dark Souls 3 Enhanced Co-op Download and install
Dark Souls 3 Enhanced Co-op.
Step 5: Launch Dark Souls 3
Step 6: Add the server to the firewall exceptions
You need to add rules to the firewall. Open Radmin VPN -> System -> Firewall Exceptions and add "Dark Souls III" to the exceptions.
Step 7: Create coop Go to the game and press "Shift" + "Tab" to start Steam Overlay. You can invite friends at any time from the beginning of the game.
Right click to your friend in your friends list and click "Join". Your friend must accept the invitation.
Join Co-op
Step 1: Install Radmin VPN and connect to the network Download and install
Radmin VPN. In the main Radmin VPN window, click "Join Network". Enter the Network Name and Password and click "Join".
Make sure you and your friends are on the same network.
Step 2: Install Painted Worlds Download and install Dark Souls 3
Painted Worlds.
Step 3: Install Dark Souls 3 Enhanced Co-op Download and install
Dark Souls 3 Enhanced Co-op.
Step 4: Launch Dark Souls 3 Step 5: Add the game to the firewall exceptions You need to add rules to the firewall. Open Radmin VPN -> System -> Firewall Exceptions and add "Dark Souls III" to the exceptions.
Step 6: Join the game Go to the game and accept the invitation. The invitation should appear in the upper right corner.
Search for a team on the Internet
You can find teammates in Radmin VPN gaming networks. In the Radmin VPN menu click "Network" -> "Join network" -> "Gaming network" tab. In the search field, enter "Dark Souls III".