Have been trying to play with a group of roommates and have had issues with them connecting and playing. We are getting the "Can't start with players not connected to each other" error and from other threads, I'm seeing, I'm guessing it's because they all share the same IP.

It’s a tricky problem - if two players are on the same network, they may not necessarily be able to connect to each other - or even recognize each other as being on the same network (as a computer is not aware of its external IP when it’s behind a NAT).

The Steam-based version of the mod offloads this problem onto Valve’s infrastructure instead.