Ranged (2) - You can actually do this quest with 2 sage, a sorc, a chanter, and 5 ranged. Sounds nuts, but it is the easiest run you will ever have. You need to have an expert leader, but it can be done. What I am trying to stress is that Ranged Rules in this quest. We often over look them but later in this primer you will see why.
Sorc (1) - The only two things that I can say are, "Don't leave home without one" and that only one is needed. Don't bring two sorc's. There is no reason to, you will be wasting a spot.
Enchanter (1) - Chanters are there for the mezz, armor and the wep buffs, tattercoat has little effect with a good sorc around. A level 60+ axe orb can tank in a pinch for 5 sec which can give the healers a chance to catch up. If the Chanter is holding a wep with a DoT on it tell him to take out his Soulbound or SoulSlayer. Mezz and confuse are the primary weapons of the Chanter here.
Damage Dealer (2) - A damage dealer is a Zealot, Dis-x Juggy, Zerker, or a level 57+ BH. However there are a number of classes that can deal good damage over level 62. You may consider them at your discretion. I would take a level 62 HK that can stay for an hour over a level 55 Juggy that says "maybe" any day. Only expert Forge Elementals allowed. Pets barely work here.
Tanks (1) - Tanks are kind of optional with 2 good healers. A high level tank is nice to have with good taunts. If you do have a tank make sure he knows his job, taunt, taunt, taunt. If a tank is not available take another sage, ranged or DD.