well, i did a quest similar to killing these charrs. It was for the Altheas Ashes (bad spelling) well there were about 25 to 30 charrs guarding the ashes. It took me (level 11 W/E and a level 12 N/E) to kill most of the charrs. But we run into problems. Those damn shaman who keep healing the charrs while they attacked up. We pretty much stop after getting a 35% DP so i run up the stair and grab the ashes and die.. it was fun.
You got at least 3 bosses to deal with and boat load of charr blade/axe storm; good thing there is no shaman around or it will take you long time to kill those charrs.
Good luck dude!