Yeah there is definitely a problem when you play with 2 people behind the same router
I can play with my brothers fine for a random amount of time but usually atleast 20 minutes but after that, one of them ALWAYS gets disconnected, then the game progresses fine when only 1 is left, this has been happening everytime so its pretty consistent.
Im on a 24/2 Mbit's connection and they are on a 10/10 Mbit's full-duplex fiber connection so the bandwidth isn't the issue here either.
The game has yet to crash when i play only with one of my brothers and another friend of mine and we've played well over 10 games at the time of this writing.
So there is definitely something fishy going on when 2 people behind the same router are playing in the same match/game.
edit:
also it should be noted that we only play games against AI, so its either been 3 or 4 players depending on if both my brothers and/or my friends are playing, so bandwidth requirements should definitely be low.
They all have good computers too (Core2Duo 2GB ram is the "worst") so the game is lag/slowdown free until the bug/player drop occurs.