Jurgen and Draco head south with the others. He would then venture a little further to see to the south. 

Quinn follows as well. Again, he’s at the back shield in one hand and torch in the other. His darts and daggers are ready for attackers. 

"Oh my goodness, what happened here?" Bryony exclaims. She kneels down next to one of the dwarf skeletons. Can she tell about how long it has been there?

Investigation - 8

Bryony examines the skeletons on the floor - a mix of dwarves and other humanoids, most of whom look like they died in combat many, many years ago.

...And that's when the swarm of batlike creatures descends from the darkness above, silently diving toward Bryony and Boona.

Roll initiative! ...But before we do...

Boona, Bryony, Ruven, and Jurgen: Make a DC 14 Wisdom (Perception) check to avoid being surprised. If you are surprised, roll your initiative at Disadvantage. (Those of you who are not surprised hear the batlike things descending to attack.)

At the rear, Quinn is automatically surprised, and must roll initiative at Disadvantage. 
Syzygy, still exiting the ancient barracks, is the last to become aware of the new threat, and will have Initiative 1. 

Batlike things' initiative: 14

Quinn’s initiative: 13 (w/disadvantage)

Perception 17

init 16

Perception - 7

Initiative (w/ disadvantage) - 5

Bryony is too busy studying the skeletons to notice the danger from above. As the bat-like creatures descend, she lets out a shriek of surprise.

Perception- 10

Boona Initiative (d)- 1

Initiative:

Jurgen: 16
Batlike things: 14
Quinn:  13
Bryony:  5
Syzygy:  1
Boona:  1
Ruven: Perception: 24 Initiative: 17 Disadvantage roll: 20

Jurgen and Ruven are the only ones with the wherewithal to act before the bat-things attack Bryony and Boona.

Initiative:
  Ruven: 17
  Jurgen: 16
  Batlike things: 14
  Quinn: 13
  Bryony: 5
  Syzygy: 1
  Boona: 1

Jurgen and Ruven are up first!

Jurgen will use green flame blade and strike with his long sword. (11 to hit with 15 damage and 5 damage to the enemy next to it if 5’)

BA Draco attack (21 to hit with 7 damage) 

Jurgen and Draco rush forward. Jurgen swings at the ones harassing Boona, but fails to connect with the tiny flying creatures. Draco has better luck, catching one and mauling it to pulp before it can bite Bryony.

Ruven is up next, followed by the creatures.

Pausing in the tunnel, Ruven hurls a mote of fire at the batlike thing divebombing Boona.
Firebolt Hit: 12. Damage: 2 fire damage.

...but just misses.

The things attack:
#3 Attack vs. Boona: 25. Hit: 4 piercing damage.
#4 Attack vs. Boona: 20. Hit: 5 piercing damage.
#5 Attack vs. Boona: 9. Hit: 6 piercing damage.

#1 Attack vs. Bryony: 23. Hit: 7 piercing damage.
#2 Attack vs. Bryony: 25. Hit: 6 piercing damage.

The pair that successfully struck Boona attach to her, continuing to feed on her blood with their long, needle-like probosces. Likewise with Bryony.
Stirges #2 and #3 found particularly rich veins (Crit damage: Boona:+1;  Bryony: +3)

Quinn, Bryony, Boona, and Syzygy are up next, in any order.

Bryony shrieks as the stirges attach to her body, draining the blood from her veins. She wrestles with the creatures, trying to rip them off her body. (Can Bryony use both her Action and her Fast Hands Bonus Action to attempt to pull the two stirges off?)

(Yes, using both her Action and her Fast Hands Bonus Action,) Bryony tears off both stirges. They flap away, dripping halfling blood from their proboscises.

Quinn, Boona, and Syzygy are up next!

Boona only realises the stirges are there after they have attached themselves, she drops her maul and begins slapping at the overgrown mosquitos attached to her..

Attack: 16 Damage: 6

( If two weapon fighting includes unarmed....I've never been able to work out if it does.)

BA- Attack: 20 Damage: 4