Narlen's Heist is an interesting little quest with some unique bits of scripting compared to most other quests in the game. As a member of the thieves' guild, he invites you along to a heist he has planned, but says to come alone and meet at dusk outside the Splurging Sturgeon.
I was having trouble getting him to spawn so I started looking around in the game's files to see how it worked. (Turns out I wasn't being patient enough.)
Narlen's script in NARLEN.DLG checks for visibility of any party members who are not thieves, and he will yell at you if any are in sight. However...it only checks for visibility of the original classes, and not the new Enhanced Edition classes, the Monk, Sorcerer, and Shaman.
So theoretically...you could meet him with a party of 5 shamans and 1 thief and he would be completely happy with that!
There are actually two separate heists in this quest and therefore two such checks to be fixed in his .DLG file.