Vesta can't get to the wraiths since she is near the back so she decides to grant a boon to one of her allies instead. She casts Haste on Davis.

Davis says "Ooo, thanks!" to Vesta and will attack the yellow one, and if/when it falls, move to the black one.

attack 1: 20 dmg 23

attack 2: 28 dmg 23

hasted attack: 20 dm 16

Round 1 (con't): (Updated map)
 - Zyl flutters in to swing at the wraiths!
 - Katarina stabs through the doorway to hit the black wraith once.
 - Both wraiths reach out for the brash fairy, trying to drain her life energy with their necrotic touch. Black flank attack: 17 Damage: 17. Yellow flank attack: 24 Damage: 28. 
(On any hit, Zyl must succeed on a DC 14 Constitution saving throw or her hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until she finishes a long rest.)
 - Davis moves past his allies into the room and strikes at the yellow wraith, nearly destroying the shadowy undead creature with his holy longsword!! 
 - Vesta sends some arcane energy to Davis, speeding up his actions and perception of time!
 - Vanizi...

Round 2:
 - Zyl
 - Katarina
 - Wraith(s)

Katarina angrily (but carefully) slashes at the BLACK wraith.

Crystal longsword vs. BLACK wraith
Attack: 24; Damage: 6 (magical slashing) + 8 (radiant)
Attack: 23; Damage: 10 (magical slashing) + 2 (radiant)

Zyl shrieks again and swings at the yellow wraith (unless it dies then she'd redirect to the black wraith).

Action:

Attack 1: 24 to hit; 18 magical slashing damage

Attack 2: 20 to hit; 9 magical slashing damage

Vanizi moves, if necessary, to get line-of-sight to one of the wraiths. She moves her Hex to that wraith then casts Eldritch Blast at the same.
(Spell Attack: 29, Damage: 9 force)
(Spell Attack: 21, Damage: 11 force) 
(Hex Damage if either hits: 6 necrotic) 

After the attack she steps back if she had stepped forward.

(Sorry. I was away on holidays in Vegas. I thought I'd have a moment to pop in and keep up but I was incredibly mistaken. Happy to try to pop in, but understand if I should sit this one out. Cheers)

 - Zyl shrieks again and swings at the yellow wraith
 - Katarina makes two well-placed attacks, opening up an opportunity for Vanizi to come in and finish off the black wraith! (Combat over!)

It appears that these wraiths were bound to the urns that were obviously broken by accident...perhaps by the cultists? Regardless, there is nothing of value in this chamber...Coming out the room, you go west to the next intersection. There is a door directly in front of you which reeks of sewage. The passage turns to the south, with corridors leading west at 15' and 30', while the main passage continues south. A shuffling cultist bearing a vacant expression moves down the corridor towards you. (Map)

Vesta follows the others down the southward passage until she spots the cultist shuffling toward them. They don't seem entirely with it so she wonders if they might just be able to walk right past the poor person. She doubts they could get much information from them.

(Can she make a Perception check to see what else she notices about the cultist?)

Perception - 17

Zyl huffs and wipes her face before following, making a mean fairy face at the odd cultist, but she is content to let them go if they don't seem to be a threat for now.

Vanizi will stay back, letting Zyl try to intimidate the cultist, if it even notices them. She waits to see what will happen. 

The cultist shambles along like a zombie, aimlessly wandering the passages. When she sees you, she just stares at you for a moment then continues to shamble along.

Katarina watches the seemingly-delirious cultist walk by with confusion.

"Um... should Katarina try to catch her or something?" the feline asks the others. "She looks to be very lost..."

Davis will use his divine sense as he approaches the cultist, if he detects that it is undead, he will give a quick warning to the party, then draw his holy sword and put the cultist to rest.

[if you want attacks. Rolling adv just in case of surprise. Also assuming haste  has dropped.]

attack 1: 7/18 dmg 11

attack 2: 16/3 dmg 18

The cultist is very much alive, just...not mentally...

Upon closer inspection, you can see a note pinned to her clothes that says, "Behold the price of betrayal..."

Will you walk on by, or interact with her? 

The passage runs 75' south, with four narrow doorways evenly spaced to the west leading to small, empty crypts. There is a door (#1) about 55' down to the east, and the passage ends in a door (#2). (map)

Knowing that they are not undead, Davis will ignore the cultist for now. He will head to door #1, looking in the rooms to the west as he goes.

Zyl will gladly just keep on going. "Ugh, they didn't even LOOK at me! What a waste. Let's just go. Oddly enough I've gotten that same look after guys have been drinking at the bar too long too late...hmm..." Zyl flutters further down the hall.

The small crypts are empty...you stand before the door in the eastern wall, about 20' from the end of the hall and the 2nd door. (What next?)

Zyl continues fluttering down making a blech sound and attempts to open the second door.