Plutonium

My brother and I are trying to play Multi custom games and every time we try to join each other it says 'joining game session' and then nothing happens. If we try to join through the friend's list it says 'playing in a private match' and doesn't let us join each other. We're playing in the same house, on the same router and UPNP is enabled. Our router also doesn't allow us to manually port forward. We used to play together all the time but not it doesn't work anymore. We can also join the servers in the browser, just not custom games. Any help would be appreciated.