We went with a pretty well equipped group of 2 mages and 1 paladin. First did allistarj. He was relatively easy and we just spammed arcane missiles and he died relatively quick. Note: All bosses are immune for all magic except for arcane and melee and if you dont use the weapon you got prior to this mission, you can't get him lower then 1%.
Sevine was a LOT harder though. Since the tank was a paladin aggro was lost relatively quick even though we had salvation on us. After wiping twice we just ignored the infernals she calls down and focused on nuking her. We had to push everything we had, potions, mana cookies, shields, cold snap, ice block, etc. But after 3 wipes or so we prevailed.
The last boss the ogre in Dreadmaul hold was just insane. The worthless lvl 47 adds around him are easily pulled and swat down, but he himself hit incredibly hard. Without a dedicated tank and healer this had no chance and we called it a night.

When your group is killing Allistarj if you have a paladin in your group, every time you use the weapon he can strike with hammer of wrath even if Allistarj still has 100% HP. it also seems to break his cast, but cant say for sure.

Just soloed as a 63 protection paly, Lady Sevine was quite hard, had to use lay on hands, but her Infernals kind of helped the dps, my reckoning was active all the way.

On the note of warlocks, Grol is actually beatable with one. Solo'd it with a 62-demo spec'd lock with gear focusing on getting crit up. (total at the time of fight was 28%) I took a slightly different approach to it...

First, firestone yourself and use demon armor. Then kill all his servants but one in the room. Send pet after Grol and nuke him with shadow bolt and use the enchanted weapon until the pet loses his attention. Once his focus is on the lock, just keep going. When your health is relatively low cast either Corruption or Curse of Weakness on the last remaining lackey and then Death Coil em to get your own health back up. Grol may be immune to magic, but the lackeys aren't.

Then back to nuking the big guy.

Took two shots doing it this way, but it worked. If you find yourself not killing him fast enough, keep at least one more instant health restorative item on hand. Potions as well as Healthstones work wonders.

All of the bosses for this quest give weapon skill when attacked, but never die unless you use the weapon given to you for this quest. If you're level 80 and can heal yourself, this is undoubtedly the best way to raise weapon skill.

Unfortunately for us Death Knights, they're immune to diseases, so you can't heal yourself with death strike and will eventually need to kill them =(

I have been working on this series for a while and finally got around to doing this one tonight as a lvl 80 fire mage.

Grol killed me several times. I'm a squishy cloth ya know. He is immune to fire and frost (even the frost nova) but not to arcane. On the 3rd try, I killed everyone else in the room first (this high, I don't attract his attention unless I tap his toes LOL). Then I ran up to him, used the staff, then starting hitting him with arcane missiles. Used mana shield to try and keep health up. Popped a mana potion and, near the end, a mana gem. FINALLY he fell. Oy.

Sevine was hard to find. When I finally did find her (she's off the side of the platform, kinda like at 2 o'clock), I forgot to use the wand so was smacked hard by her and the whatevers she calls up. Ran off until their aggro dropped then healed and tried again. This time, I killed everyone off, ran up to her, smacked her with the staff, then hit her and only her, with arcane missiles. I ignored the big whatevers and just kept hitting her. I kept close enough that whenever the cooldown of the wand was up, I hit her with it again. At one point, the message did come up that the felcurse was working, but I was too busy to notice it until later. Arcane spells are mana hogs so I had and with the mana shield also going, I managed to partly use evocation and a mana gem. Finally she went down, I quickly looted her, hit slow fall, and jumped off the cliff.

Allistarj was the easiest for me. Probably because he is ranged like me. I decided to switch to my arcane spec so I could hit him the hardest with the missiles. I also kept on my gear until near the end. I got him down to low health, switched to the wand, kept hitting him until the cooldown was up, then ran up and hit him with the staff.

To correct myself, hitting with the staff does nothing. Instead, I put the staff on the action bar and just hit the button to ""use"" it. I had to be really close to the target for the use to work. That's how Grol kept killing me. I thought I just hit him with it (that's what I get for skimming the info here vs reading it). Ha.

I'm saving the last bit until my sis-in-law lvl 80 DK can come help. Yes, I am going to take the easy way out. I'm a wimpy gnome cloth covered squeaky toy.

im not able to loot the necklace, not sure what the deal is? I have my quest sword and i use it and i can kill them, but none of the three dropped a necklace for me. Is there some part of this im not understanding?

I took this quest at the beginning of December, 2009 while working on the Loremaster achievement. In many attempts both solo and with Paladin friends I was unable to kill Sevine or Grol. I could reduce them to 1 HP but no further. What finally became clear was that, as has been stated here before, the Fel Weapon is not essential for killing the 3 MOBs holding amulet shards, the Fel Salve is the essential element. I did this as a very well geared L80 Mage. Here is the procedure for completing this quest:

1. Do the preceding quests and obtain the Fel Weapon.
2. Upon obtaining this quest also get the Fel Salve. It has 5 charges.
3. For Grol: Clear the room around him until he's left alone. Get within range (he will aggro) and apply the Fel Salve. Attack him with or without the Fel Weapon.
4. For Lady Sevine: Clear the MOBs immediately around her then proceed as with Grol. Use AoE spells or some other form of crowd control to finish off Sevine and the demons she summons.
5. For Alistarj: Kill your way into his position inside the cave. Clear the MOBs nearby and repeat as with Grol.
6. Return to the Fallen Hero to turn in the quest.

It is not necessary to use the Fel Weapon but having gone to the lengths required to get it, I think it's a bit silly not to use it at least once. But the Fel Salve is what enables you to kill all 3 holders of the pieces of the amulet. The weapon is just the end of the wild goose chase you're sent on in order to get this quest.

As of 3.3.5 the 10 minute cooldown on the weapons is removed. No reason to get the salve unless you sell/destroy your weapon. (Staff vendors for 5 gold, huzzah!)

I just ran all three within 2 hours using a lvl 61 Pally solo. I didn't need any salve, but after killing Sevine I couldn't loot her, so I ended up logging out of the game and going right back in and I was able to loot the quest item at that time.

Soloed this as a level 62 warrior. For some reason I couldn't loot Grohl. I got Allistaarj's amulet no problem. I'll let Grohl respawn and see if the amulet drops this time.

Don't forget to use your weapon ability on the bosses for this quest!

As no one have posted any information about it:

This quest DOES count toward Loremaster of EASTERN KINGDOMS