Kei 

Wheezing as the poisonous gas penetrates his lungs, Kei closes his eyes and visualises the space between the two circling horrors. He pictures that space exploding with energy that catches both in its blast. When he opens his eyes they are as black as the darkest shadow. As the colour returns to his eyes a flickering of light forms between the two birdlike creatures. As in his mind, it explodes outwards engulfing his enemies.

Meanwhile, at sea level, his tentacle flails at the shrieking horror (if it's within range or within 30ft movement plus range)

A - casts Synaptic Static for 25 psychic damage, plus roll 1d6 and subtract from attack rolls and ability checks. ½ damage on INT17 save and no rider effects

BA - tentacle moves/attacks the shrieking horror 20 for 9 cold damage.

CON save to shake off the poison 23

Kellen may roll a fresh DC15 CON Save (vs. Poisoned.)

Flying things: DC17 INT Saves vs. Kei's psychic blast: 8, 17, 3

The first badly-wounded vulturelike creature dissolves into ichor, while the two in the air shriek in pain, one noticeably more affected than the other.

Nevertheless, both wheel around, drop, and attack.

#2 Shred Attack vs Kellen: 24. Hit: 9 Piercing damage plus 14 Poison damage.
#2 Shred Attack vs Kellen: 19. Hit: 11 Piercing damage plus 13 Poison damage.

#3 Shred Attack vs Tamra: 18. Hit: 11 Piercing damage plus 7 Poison damage.
#3 Shred Attack vs Tamra: 22. Hit: 12 Piercing damage plus 12 Poison damage.
(It then tries to shake off the effects of Kei's spell: DC17 INT Save: 12

Already stunned, Tamra is torn open. She collapses on the deck, dead.

Kellen, barely shaking off the Stun effect of that horrible scream (and perhaps the poison, too, if he makes his new save) may act next!

1 4

Kellen

Almost eviscerated as well, Kellen plays a quick, jaunty tune and sings of rejuvenation. The enchantment interlaced into the words takes hold, and his wounds begin closing up.

Healing word: 21

He then wheels around, quickly changing the tune into an exciting romp, and a blast of fire issues from the mandolin towards the creature that attacked him.

Attack: 15 Damage: 21

(Forgot to roll con save: 14)

(Other roll for disadvantage on attack roll: 14)

The horrid beast squirms in the air, and avoids the brunt of Kellen's arcane flames.

Finished re-rigging the tiller, Rurik abandons it and runs for the ballista, which he loads and swings around.

The massive wormlike creature moves closer, from the east. The warship speeds toward you from the north.

Two vulturelike monsters flap their black wings and remain within melee distance of the deck.

Gerrard and Kei may act! (Still poisoned, they have Disadvantage on all attack rolls and ability checks. You may attempt a new DC15 save at the end of their turns.)

Gerrard:

Dropping the bow and drawing his blades, Gerrard moves towards the beasts, deftly switching places with Kellen and moving into melee range with both vultures even as he moves his ally out of melee range.  His dagger flares to life with foreboding flames as he settles into a defensive stance!

Bait and Switch AC add to Kellen:  7

Bonus action to ignite dagger

Action to Dodge

Constitution Save versus Poison:  22

Kei 

Now with the flying death birds close by Kei decides to cast more defensively, hoping to aid Gerrard in his close combat. He wills his own mind to strike at both birds before cracking an imaginary whip at them. Once his magic is cast he backs away from the melee*.

BA - Cast Mind Sliver with Twinned metamagic on both vultre-like creatures. Take 12 psychic damage and subtract 1d4 from next save. INT17 save 

A - Cast Tasha's Mind Whip at 3rd level, striking both birds.  Take 13 psychic damage and suffer various effects. INT17  save for ½dmg and no riders.

M - Only if he sees the bird closest to him suffer from Tashas Mind Whip. If it needs to be a Readied movement, so be it. Wasn't sure if he could, within his turn, move after casting AND witnessing the birds reaction.

Kei

CON save 23

Twin horrors' INT 17 Saves vs Kei's Mind Sliver: 11,  15

Followed by: INT 17 Saves vs Kei's Mind Whip: 11,  8

Both birds writhe from the effects of both of Kei's spells. Kei takes advantage of the situation to retreat to the far side of the forecastle.

#3 (which killed Tamra) screams in pain and frustration. And then it SCREAMS. (Stunning Screech)

Gerrard and Kellen: Make another DC15 Constitution Saving Throw. Failure: 11 Thunder damage, and you (again?) have the [condition]Stunned[/stunned] condition until the end of the demon's next turn. (Kei and Rurik are just out of range.)

#2 continues to tear into Kellen:
Shred Attack #1 vs Kellen: 11. Hit: 15 Piercing damage plus 14 Poison damage.
Shred Attack #2 vs Kellen: 21. Hit: 10 Piercing damage plus 11 Poison damage.

#3 horror DC17 Save vs. Kei's earlier Synaptic Static: 16

Kellen is up next! (But make that save first!)

>Gerrard moves towards the beasts, deftly switching places with Kellen and moving into melee range with both vultures even as he moves his ally out of melee range.

Except, of course, that Gerrard had switched place with Kellen in a defensive pose...

Disadvantage (Dodge) rolls:
Shred Attack #1 vs Gerrard: 9. Hit: 15 Piercing damage plus 14 Poison damage.
Shred Attack #2 vs Gerrard: 24. Hit: 10 Piercing damage plus 11 Poison damage.

(Nudge to resolve rolls)

Gerrard:

Doing his best to protect his friends even as the demonic vultures attack, Gerrard tries to steel himself against the sonic scream!

Constitution Save:  10

Gerrard Indomitable -- really doesn't want to be stunned!

Constitution Save:  7

Kellen

Kellen has a flash of remembrance, just before the next screech attack. He steels himself for what he already knows is coming: (using 18 portent roll)

Nodding thanks to Gerrard and trying to catch his breath, Kellen tries to fight the poison: (5 was rolled)

But fails, and the poison continues to seep through.

He once again utters a string of healing enchantments that quickly turn to insults aimed at the vulture. Back off, you overgrown turkey, go choke on a worm!

26 HP regained, vulture needs to make a DC 17 Wisdom save or take 8 psychic damage and have disadvantage on the next attack.

Gerrard and Kellen shake off the scream (Kellen with the aid of foresight, Gerrard through sheer force of will.) Both remain poisoned.

Vulturething #2 DC17 WIS Save vs. arcane mockery: 7

Rurik struggles with the ballista, swinging it around and taking careful aim. The serpent thing surges closer; so does the Feldren warship.

Gerrard and Kei may act once again.