I just went through this dungeon with a few GSCH folks, and I honestly feel the dungeon is rather difficult. I poked around on the internet, and I found some handy tips for those venturing into this abomination.
The two key difficult parts lie in the Second Champion, and Faolain herself.
During the second boss, he will summon nightmare spiders. Your only hope for success here is to circle strafe the boss. The spiders will focus on one or two people, but moving as a group to prevent accidental death will help. DO NOT TRY TO RES ANYONE DURING THIS FIGHT. It will only lead to death and a very long run back.
During the Faolain encounter, you must defeat ghostly images of the fellow members of Destiny's Edge. Eir should be your first target. Once you kill one, Faolain will drop down to try to res her. If you do enough damage to Faolain, she will retreat.. leaving 4 members left. Rytlock should probably be next, but consider Zojja a threat as well. Repeat the process of preventing Faolain from ressing them as you kill them, and the fight will move forward.
I hope this helps those who venture into the depths of Twilight Arbor. Not knowing this when I went in, and banging our collective 5 heads against a wall really ruined my day. I hope you can avoid the same fate.
