At first I was trying to figure out whether they can go back to previous hall and use those shelters or not. Then I noticed that there was a mistake in chapter 2; In one panel, the door was close, where it wasn't in another panel. I'll assume they can't but there would be no room for a loop hole.
But if by any chances they can, there exists a loop hole, or I dare say, a solution to this game. Currently there are 6 players, 5 shelters, and 5 halls left including 2nd hall (assuming the game will continue until 1 shelter left). That make 15 shelters for a total of 5 round, which mean 3 people can survive if 3 people agree to die in this round and have people who want to survive use up their "death" cards.
2nd round (5 shelters)
3 used, 2 unused, 3 players survive
3rd round (4 shelters)
3 used, 1 unused, 3 players survive
4th round (3 shelters)
3 used, 3 players survive
5th round (2shelters)
2 used, 1 used from the 4th round
6th round (1 shelter)
1 used, 2 used from the 2th round
I think 3 players max can survive this game, which is so kind of a GM, and cruel because there has to be an agreement beforehand.