Hamachi - Can only play with 3/4 people

[Kolath]

I've been trying to get some multiplayer FfH2 going with three of my friends. They all live in the same apartment and share a router and internet connection. We have tried using Hamachi but have found that only three of us can connect at any given time. The three of them can play together or I can play with two of them. But the fourth person can never connect.

I have successfully connected to each of my friends individually or in pairs, but not all at once.

Any ideas? Hamachi offers no help. I can sometimes ping all of them or sometimes one of them randomly will be un-pingable.