Ash cautiously leads her comrades through the left tunnel until they reach the room where the carrion crawler fought them and where Talsarios used his spell to put the archers into a slumber.
Once Nathros and her have secured the room - Artanis and Mycah can help, so long as nothing jumps out at them right away - Ash will ask Mycah to climb first this time, since they know a little about what to expect. She'll also give him her rope and then explain.
"If the ...carrion crawler?... returns while we're climbing, it'd be safer to have a rope to haul the remaining people up as quickly as possible, rather than have them risk rushing their climb. Plus, you and Artanis can use your bows to distract it or shoot any foe that may approach down that tunnel before we all arrive at the top. The others can try the oil and fire down here - less chance of the oil splashing onto each other with a toss from a lower height. "
"Before we all go through to the other end, however, I expect the gang or cult to have a different arrangement as they guard the area. Perhaps some of them will hide in the tunnels or have an alarm set to go off as we enter. Let's all try to be quiet once we get to the top. Perhaps we'll hear them before they hear us."
Were I in their shoes, I'd have scouts waiting in the tunnels quietly. I'd have them report back immediately upon sensing the enemy - in this case, us - and avoid engaging in battle. Then, my group would rally by the time the enemy closed in and we'd be on guard, have cover, and have traps and the like. If they're smart, they'll have done even more than that. I don't expect this will be easy.
I suppose some of them may perhaps think strangely enough and be glad to die for their immortal or necromancer so they may be raised to serve even in death... I hope they're not that far gone. A foe without fear of death... Ash will randomly shudder a little to herself while the elf and the scout climb up, so long as they agreed with her suggestion, that is.