An ape appears from the tiny fuzz ball that Renee threw at Sahuagin 7. It thumps it's chest, ready to fight next turn! 

Sahuagin 11-15 move into action and try to rush the party. Sahuagin 11 and 15 moves 30 feet and takes the Dodge action. Sahuagin 12 moves 30 feet and attacks Mackenzie. Sahuagin 13 and 14 moves 25 feet and attacks Brazzak. 

Sahuagin 12: Bite Attack: 10 Damage: 5
Sahuagin 12: Claw Attack: 4 Damage: 5
Sahuagin 13: Bite Attack: 16 Damage: 2
Sahuagin 13: Claw Attack: 18 Damage: 3
Sahuagin 14: Bite Attack: 11 Damage: 5
Sahuagin 14: Claw Attack: 15 Damage: 5

Heilamin, you're up! Modron follows closely after the first mate and a Sahuagin Champion.

Heilamin begins an incantation under his breath, and thrusts his lute forward casting Thunderwave at 4th level such that it encompasses Sahuagins 12, 11, and 13. Damage: 32. DC 15 (and is pushed 10 feet away from you. On a successful save, the creature takes half as much damage and isn't pushed.)

("Not so close! When courting someone you only go 90%, let them come the other 10. Back off." And he smiles.

Sahuagin 11 CON Save: 6
Sahuagin 12 CON Save: 18
Sahuagin 13 CON Save: 12

Heilamin bursts a loud BOOM from their fingers. You clap Sahuagin 11 and 13, they fall limp. Sahuagin is heavy wounded and pushed back 10 feet, tumbling over into the rowboat. They are knocked prone.  

Sahuagin Champion 2 moves up and takes lunges wuth their spear held in two webby hands at Heilamin and flinging two of their warriors like rag dolls.

Champion 2: Attack: 9 Damage: 10
Champion 2: Attack: 16 Damage: 10
Champion 2: Attack: 8 Damage: 8

The first mate parleys with the Sahuagin in front of them and lunges with their rapier.

First mate: Attack: 22 Damage: 2

Heilamin, for a great quote take Inspiration!

Notwithstanding Heilamin's subsequent spell Mackenzie would have taken the reaction attack as Sahugin 12 moves to engage Mackenzie. It is greater with a reach attack (Polearm Master reaction) from his Halberd, thrusting straight toward it as it gets within 10 feet of him calling out "You have sealed your fate...so be it"

Attack: 24 Damage: 7

Crit!  MacKenzie, on feeling the power of the strike, whispers a quick prayer to imbue the strike with additional power and smites the creature for an additional 28 radiant damage as the strike pulses with divine power for a total of 31 damage to the unfortunate Sahugin that charged  at Mackenzie.

Also, on a Critical, Great Weapon Master says another melee attack can be taken as a Bonus Action....would this apply now or when it was his turn in initiative order?

Mackenzie obliterates the Sahuagin who entered his space. The creatures bursts from the radiant energy into a slimy goo on the ground. 

-On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.

Since the wording does not say "when you make a melee weapon attack action, I would say you can use a bonus action attack when it is your initiative count. Where I don't think this counts is if you use a reaction after your initiative count, because you've already taken your turn. Hope that makes sense!

Modron, you're up! Followed by Mackenzie.

Round 1 Initiative order:
Captain Andy
Renee
Sahuagin 11-15
Heilamin
Sahuagin Champion 2
First mate
Modron
Mackenzie
Sahuagin Champion 1
Brazzak
Sahuagin Champion 3
Sailors 1-4
Sahuagin 1-5
Sahuagin 6-10

Modron is amazed at the throng of creatures.  He  carefully chooses a point where he can hit creatures but no allies and sends a meteor streaking to that point where it explodes and any creature within 5 feet of the explosion takes 8 fire damage on a failed DC 14 dex save or half that damage on a successful save.

Modron will stay where he can see the action but is as far from it as possible.  There are 5 more meteors circling Modron as he prepares to help his friends.

(Wow, wimpy meteor!)

After impaling the Sahuagin on the end of his halberd, he find himself pulled forward as the energy of the thunderwave spell catapults the dead creature backwards off the blade.  Turning that momentum into a spin Mackenzie closes to attack the Sahuagin Champion (2) bringing his weapon down from a high arc before following through with additional thrusts.

Bonus Action (carried over from GWM strike): Attack: 22 Damage: 6

Strike 1: Attack: 21 Damage: 5

Strike 2: Attack: 13 Damage: 7

Unfortunately there are no space that hit multiple creatures that does hit either Renee's ape or Brazzak.) Modron lobs a meteor at the space near Sahuagin Champion 2 and it explodes in a fiery blaze. 

Champion 2 DEX save: 3

Champion 2 sees the meteor coming, but trips on a loose board trying to dodge out of the way. They take 2 fire damage, but are knocked prone from the blunder. 

Champion 2 is prone when Mackenzie advances. Additional rolls are for the advantage gained on a prone creature using a melee attack. 

Bonus Action: 13

Strike 1: 16

Strike 2: 13

Champion 2's AC is 16, the bonus action attack misses but you land the other two strikes dealing 14 damage!

Champion 1 bears it's razer sharp teeth at Captain Andy and strikes with it's spear, holding with both webbed hands. 

Champion 1: Attack: 16 Damage: 7
Champion 1: Attack: 20 Damage: 6
Champion 1: Attack: 16 Damage: 7

Captain Andy lifts his scimitar at just the right time and parries the first attack. Champion 1, thrown off by the block, misses their second but lands the last hit. 

Brazzak, you're up!

Unlimbering his Greatsword, Brazzak steps in and attacks two foes!

(Sahaugin 15 has action dodge, so I will make first attack at them for a miss.)

Brazzak swings and misses Sahaugin 15, but a swing on 14 lands dealing 10 damage.

Champion 3 moves up to Mackenzie and takes three lunges with their spear. 

Champion 3: Attack: 12 Damage: 10
Champion 3: Attack: 11 Damage: 6
Champion 3: Attack: 8 Damage: 4

The sailors do their best to fend off the Sahuagin. As they swing their swords...it quickly becomes obvious this is not their specialty. 

Sailor 1: Attack: 18 Damage: 2
Sailor 2: Attack: 4 Damage: 3
Sailor 3: Attack: 19 Damage: 1
Sailor 4: Attack: 15 Damage: 6

Sahuagin 1 presses on the first mate and attacks them. Sahuagin 2-5 all stand guard of the upper deck where Captain Andy is and take the Dodge. Any attacks against them are at disadvantage. 

Sahuagin 1: Claw Attack: 16 Damage: 2
Sahuagin 1: Bite Attack: 20 Damage: 3

Sahuagin 8 takes the Dodge action on the upper deck where the bow is. Sahuagin 6, 9, and 10 attack the sailors. Sahuagin 7 looks overboard and speaks in a language you all don't understand. After a few moments, a large shark shoots out of the water and bites at the sailor near the edge of the deck. Then, Sahuagin moves to attack the Ape. 

Sahuagin 6: Claw Attack: 22 Damage: 4
Sahuagin 6: Bite Attack: 18 Damage: 3
Sahuagin 7: Claw Attack: 12 Damage: 4
Sahuagin 7: Bite Attack: 21 Damage: 3
Sahuagin 9: Claw Attack: 19 Damage: 5
Sahuagin 9: Bite Attack: 13 Damage: 3
Sahuagin 10: Claw Attack: 21 Damage: 5
Sahuagin 10: Bite Attack: 16 Damage: 5
Hunter shark: Bite Attack: 19 Damage: 15

All of the sailors miss their strikes. They are then swiftly killed by the Sahuagin's bite or claws....and one is swallowed whole by a 15 foot shark that then dives back into the water creating a splash of water about halfway of the main mast. 

Round 2 Initiative order:
Captain Andy
Renee
Sahuagin 11-15
Heilamin
Sahuagin Champion 2
First mate
Modron
Mackenzie
Sahuagin Champion 1
Brazzak
Sahuagin Champion 3
Sailors 1-4
Sahuagin 1-5
Sahuagin 6-10

Captain Andy continues to press on Champion 1
Captain Andy: Attack: 10 Damage: 5
Captain Andy: Attack: 20 Damage: 4

Renee, you're up!

Renee will move up to Creature 14 and attack with her rapier. 

Attack: 24 Damage: 10

 As a bonus the Ape will attack Creature 7. 

Attack: 13 Damage: 7

Attack: 25 Damage: 12

Sahuagin AC 12. You miss with your rapier (and yes you would have gotten the sneak attack damage for Brazzak being within 5 feet), but your ape hits both slam attacks. Sahuagin 7 looks heavy wounded.