The back room is divided into three sections: left, middle, and right. In this map, the red dots are the left pads, the green dots are the middle pads, and the blue dots are the right pads:


In each of the three sections, there will always been exactly two callers that need to be revealed and killed, for a total of six.

Once both callers in a particular section have been revealed and killed, all of the remaining braziers in that section will extinguish. This is the way by which the game signals to the player that they've completed a section and that any remaining braziers in that section should be ignored.

The map above shows my preferred path for running the two sides: pink lines for the left runner, and teal lines for the right runner. Yellow lines are shortcuts that can be taken, if a particular section is completed early, before revealing all of the braziers. I prefer this particular path because the two runners' paths meet in the middle, meaning that if one side finishes their route before the other (this is quite common; one side might get lucky with finding the callers early while the other side is gets unlucky and reveals multiple assassins), they can seamlessly run their partner's path backwards.

As for the assassins, they should be killed if they are aggroed on to you, particularly since they apply a very nasty snare. However, there will be rare cases where the assassin does not aggro onto the player who revealed it and will instead chase after the other player (even if they're on the other side of the room). If that happens, don't chase after it; just let the other player know that they might be getting some company in a bit.