there's a timer associated with the spawnable mobs, not sure the timer
Two Sirens are 45^^^ and it seems you can no longer shake them.... Edit
Ran past the Sirens but could not shake them. So unless you can beat these two 45^^^ Heroic singing ladies you are dead... like me. This brings into question the possibility of completing this quest solo.
All you have to do is run up the climbable wall near where the named spawns. The to adds will run back --Virii 01:29, 1 December 2007 (UTC)
Run past to the ledge beyond Edit
There is a small shelf that looks like a drop off that you can ditch the sirens. Be carefull not to fall into the sea again, however.