Six of these, they're the hornblowers behind the Guardian of Glorification. When the event starts, they are targettable but unaffectable. When the Guardian reaches ~90% (I think it was between 91 and 93%), they become affectable with the messages: "The sounds of life emanate from the center set of horns" "The sounds of power emanate from the right set of horns" "The sounds of ___ emanate from the left set of horns"?
Once these become affectable, you need to drop aggro on the name (we do this by having everyone run to SE corner and letting enchanters memblur).
When you've dropped aggro on the Guardian, you can have a few DPS people get invis and lev, move into the room, run up the horns to the Bolsterers platforms, and kill the Bolsterers. Guardian does not see through invis, Bolsterers do but they don't attack. Make sure these people stay on the platforms: if they come off they're in danger of aggro'ing the Guardian. The bolsterers do not attack at any time, so your DPS can just kill them at leisure while the rest of the raid waits in the hallway.
These are the horn blowers behind the Guardian of Glorification. You cannot attack them before the event begins. There are six total. To begin the event, you hand in the key you formed through the dungeon (the pieces drop off the visionaries and sentinal), and the Guardian will become active. About 50% into the battle with the Guardian, he will split. After he splits, the Bolsterers will become killable. Anyone can invis up behind the two split guardians and murder them. They have a lot of HP, high AC, and don't attack back.