OK here is what to do:

Target ghost, use zapper on them, it aggros them but they die after about 10 secs. Then 1-4 (I had 4 at least twice) "Restless souls" appear. You target one, use zapper again and again after 10 seconds they say "thanks to egan" "rivendare must die" etc and become "freed souls" repeat x15 and you do quest.

It was slightly bugged for me and stuck on 14/15 but when I logged out/in it was completed.

I can't believe nobody's mentioned the Ghostbusters reference with Egan, not to mention how the blaster looks when you fire it.
"Don't cross the streams!"

Some additional information:

You can stand (at 59, anyhow) right near the entrance inside of the Live side, and not get aggro from the first pull ofr level 55-56 skeletons. If you look forward, you can see where the wall for the gates stop and the hallway begins. This is where you want to be. Be careful about running too far ahead, because the gates for the entrance close down behind you, and the only way out is hearthing (or dying).

Be careful, because if you don't tag the mob immediately with the blaster when they're in range, they might walk out of range before the 2.5 seconds of channeling that's required elapses. You can stop some of them with /dance, but(!) they will not allow you to tag them with the blaster, while they're dancing, so it's kind of pointless.

The mob will run at you, and maybe get in a hit before it "explodes" into often one, but I've gotten up to four, wisps that are Restless Spirits.

These spirits will flicker around pretty wildly, and you have to tag them again with the blaster to get credit. The channeling effect will make it so that you will always be pointing at the spirit, so you don't have to manually try to keep it in front of you.

Timing from my chat log, the Spectral Citizens show up roughly 8-9 minutes apart, so assuming you only get one wisp per pull, that's 2 hours of sitting at the entrance. I managed to get all mine in just over an hour, though (one pull had 3, another had 4 wisps).