Underworld Unwanted Guests quest bugged?

So I was farming with my friend necro in UW, and after cleaning all Aatxe and Smites we decided to do Unwanted Guests quest.
We killed all 3 patrolling Terrorwebs and I aggroed all 3 invincible Aatxes while my friend killed that Keeper of Souls. Quests says that they will die when we kill Keeper of Souls, but all 3 were just standing there hitting me and we couldnt target them since they were invincible.
Is it bugged or we did something wrong?

Sometimes it takes a while for the Aatxes to die. It is possible to kill all of the Terrorwebs without aggroing a single Aatxe, so it's not too important.

My understanding is that after the keeper dies, the attaxes (sometimes) won't die until they have gone outside all aggro circles then they just drop.

Not too sure of this myself as I have only attempted the quest once.

The quest has always been this way.

Like Cherno says, if the aataxes have a target in aggro, they will not die. Easiest way to do this quest is as Savio mentions, but if aggro must be engaged, use a tank to hold the aataxe while another person teleports the team using the reaper. Of course, this also means making sure that the reaper is not in aggro, too.

Ah I see.
Do they also drop items when they die?

No, since you don't directly kill them.