Hey there. You have the first plaque to open the door in front of the chest right of the door (i think ou found id.) Once the door openned, you have another plaque on the ground under a torch.
just make your 3 other guys comes the corridor, leave the first plate to reach the door, walk on the other plate in the other side and it's open again :) I'll think about a clue in a future updates. Do not hesitate to let'me know if there is something else !

Ok. You got me. I can't get past the first door puzzle. There is no way to hold the door open and my party can't transition to the next map without all four characters.