Honestly at this point, I have no idea how a 2 vs 2 work, but just thinking that from the the flow of the story, having a 2 vs 2 would make more sense than having two separate games going on (or it is indeed two separate games, and somehow the results of each affects the other, aka the catastrophe maybe?). And catx3, Veshv, I completely forgot that Shion and Manabe were the referees of Hal and Fukurou, so that would also make sense since like you guys mentioned, there is no way they would be far away from their target unless they were somehow close by and being monitored already.
Edit: If I have to add one more thing, Fukurou was known to be the Poker master of this series, so it would make even more sense if the was somehow involved in this "poker" game. This is more of a wild guess from a storytelling perspective since what better way to beat Fukurou than to beat him at his best game?