Vincent was probably around C7.

initiative 5 

Vincent is readying himself to lay waste and retreat. 

I'll be in I8.

Wisdom Save: 19

Just to clarify, the squares on the previous map are 10 feet, rather than 5 ft, so four PCs/NPCs can actually fit on each square. Because of social distancing everyone seems to be giving each other space so far, which is good.

We have moved fairly quickly, so I'll wait for about another hour before starting combat.

My understanding of the initiative order and locations for PCs (and NPCs that I've shared so far) are:

Let me know if anything is incorrect. Ervalin will go before Tarhun, because he has a higher dex. Reguh and Beatrice have the same dex, so I'll get you to each roll a d20 and highest number goes first.

Looks about right to me :) 

10

The above is the battle map for the combat, which starts now.

I tried to balance the encounter to take into account the large number of players, but it is now showing up as 'deadly', so good luck. There are allies and a very strong rival from backgrounds in the battle. The allies will help you get through (hopefully), though you will likely need to burn some resources including healing spells to keep everyone up. To increase the potential for survival, I suggest that you ignore the Thief/Thug at least for the moment.

Given the number of people in this combat as well as in the campaign, I'm going to group initiative into groups of 4; so Laire (21), M3 - Oden knows him as Cuhnus (20), the Thug (20) and Oden (19) all go first.

That ... could not possibly be part of the show! Even Laire could understand that. And the man in front of her was in a terrible danger. Cursing herself for giving in to heat and relaxed atmosphere, that made her unarmoured, Laire did the next best thing she could think of - grabbed a few pebbles from the sand:

Bonus action: Magic Stone

Action - attack S5: Attack: 10 Damage: 7

The stone bounces of the creature's rubbery hide and it turns to Laire and snarls.

Cuhnus takes two attacks on the creature in front of him with his longsword: Attack: 18 Damage: 4

Attack 2: 17 Damage: 3

The attacks hit

(for brevity, I'll assume I can see S2 emerging from the water, but if my view is blocked, I'll edit my action)

Oden jumps clear of the currents to see the fish-faces rise from the water. He bring his longbow and an arrow forward and shouts to Ervalin, who was also readying his weapon, with the authority of the elder brother: "Get Mira and our brothers to safety. Don't come back until they're safe. I got this." He lets the arrow fly towards the closest enemy.

Attack: 10 Damage: 6

He then starts making his way towards Elanza and Joao through the fleeing people.

Oden's arrow goes wide

The thug's posture changes when the screams erupt from the beach. He drops his drunken guise, looks at the creatures emerging from the water and shakes his head before running toward the shoreline. [He is not within Tharhun's reach for Tharhun to grab him.]

Movement: 30 ft North. Attack on S5: Crossbow 8 Damage: 7

The crossbow bolts sink into the creature's flesh.

Next up are M2 (17), S7 (15), Joao (13), S6 (11)

M2 - Nahnir moves along the shoreline until she is in melee range with S4 and swings her sword with two hands on the creature: Attack: 9 Damage: 10

The attack hits and the creature looks very hurt with just this hit

S7 moves up to Mi3 and makes a bite Attack: 20 Damage: 2 and a claw Attack: 15 Damage: 2

Both attacks miss

Joao stabs S1 with his spear (using two hands) twice, Attack 1: 18 Damage: 9 Attack 2: 22 Damage: 3

The first attack hits, the second misses

S6 moves around to Mi2 and makes a bite Attack: 12 Damage: 2 and a claw Attack: 19 Damage: 5

Both attacks miss

Up next Tharhun (10), Ervalin (10), Arvastan (8) and C1 (8)

 Ervalin shouts back at Oden "I don't take orders from you any more brother. I will keep them safe, but you will not get all the glory for protecting the island." Ervalin moves back to grid position W5, putting his body between the siblings and the danger coming from the sea and he unleashes an arrow from his longbow. Attack: 7  Damage: 3

Miss

Arvastan runs out of the tavern, sees his siblings and what is happening on the beach and (to Oden's surprise) releases a mote of fire (fire bolt)at S2. Attack: 20 Damage: 9

Hit

One of the creatures looks different to the others, carrying a wand rather than a weapon and dressed in a cloak. She moves up to the shore and starts chanting and gesturing, before something catches her eye. Reguh, the creature seems to be staring at your blue robe.  She suddenly shouts at you in a strange language that you somehow understand as "Approach." Reguh, roll a wisdom saving throw (DC11) vs the command spell.

[I didn't think through running so many NPCs, a lot to get through.]

Aliez, you are in the next group of 4 after Tharhun.  

Seeing the thief escape his readily available grasp, Tharhun grits his teeth slightly, before moving to dash around the crowd, to get as close as possible to the creatures attacking the shore. As he likely won't be able to reach them this turn, he simply uses the distance remaining to ready his cloth covered weapon.

Wisdom save with advantage due to being a gnome. 20

Reguh feels a sudden pull to approach the strange creature, but resist.

Aliez leaps up from her blanket, "I apologize but our fortune telling will need to stop here." She runs towards the beach (to S4 30ft) and calls out to Vincent, "Your god better give us a hand!" (Bardic Inspiration 1d6 for Vincent). Looking over at the cloaked wand wielding creature, Aliez begins whispering horrible secrets, the creature must make a DC14 wis save or take 16 damage and uses it's reaction to run as far away from me as it can. If it makes the save takes half damage and doesn't run. (Dissonant Whispers) 

The crowds have started pouring towards the town centre and towards the dock and are now thinning, so Tharhun, you make it just past Halla on the beach. Given your proficiency in nature, you know these creatures to be Sahuagin, vicious creatures that have been known to kill entire villages before. You know to be careful when battling such a creature. 

 [Sorry, the thief was 5+ foot away from your reach, though it may be for the best, as he seems to be helping defend the island for the moment.]

Oden, you have fought Sahuagin before, including when you were in the Militia. Usually their attack tactics aren't this effective or well organised and the more senior members of the militia and Shark Hunters can usually take care of a few Sahuagin and the rest will scatter. This year is different, with a number of the Militia and Shark Hunters disappearing before anyone knew the attack was happening. 

S3 attacks Joao, making a bite Attack: 13 Damage: 5 and a spear Attack: 22 Damage: 7

S4 attacks M2 (Nahnir), making a bite Attack: 10 Damage: 5 and a spear Attack: 17 Damage: 2

The Sahuagin's spear finds its mark and Nahnir coughs out blood, quite hurt, but still standing. The Sahuagin gets a thirsty look in its eyes, urged on by the sight of its prey's blood.

Elanza makes one attack with her spear at S2 (using two hands): Attack: 19 Damage: 13 and a second at S3 Attack: 16 Damage: 6

The first attack hits and looked powerful enough to kill most people who saw it in one blow, yet the Sahuagin remains standing. The second attack cant pierce the Sahuagin's rubbery skin. 

[Because Joao is damaged by the first attack and no longer has full, health, the creature gets advantage on all subsequent attacks, going into a blood frenzy. Second attack advantage roll: Attack: 5 Damage: 2 ]

Up next: Vincent (5), S1 (5), Reguh (4) and Beatrice (4).

Beatrice make a (DC10) Wis saving throw at the start of your turn, if you fail (unless you roll a 1 or 2) your movement action must be to get out from the building in the most direct route as possible and to follow the pull of the crowd. You can then take your action to do anything you would like (including as a dash out from the crowd).

I like your idea of a very low number meaning you are paralysed with fear, so I'll use that if you roll a nat 1 or 2 again.

Wisdom saving throw for Sahuagin Fanatic: 20

The creature screeches in pain as it takes the full damage and it will run (or swim) away from Aliez on its next turn. [Great turn!]

Wisdom saving throw: 9

Hearing the sounds of the combat around her, Beatrice loses the last grip she has on her temper, and flies into a rage, losing the last of her fear. Hefting her axe, she forces her way through the crowds, ducking and weaving around legs and shoving where needed (double dashes) towards the beach into melee range with S6 (to S3), holding her axe at the ready.

Quote from catbert >>

Hearing the sounds of the combat around her, Beatrice loses the last grip she has on her temper, and flies into a rage, losing the last of her fear. Hefting her axe, she forces her way through the crowds, ducking and weaving around legs and shoving where needed (double dashes) towards the beach into melee range with S6 (to S3), holding her axe at the ready.

 
Unfortunately with Beatrice’s little gnome legs (25 foot movement speed) and the crowd still counting as difficult terrain (the parts in grey cause half movement), Beatrice only makes it U5... Unless she wants to vault over the table to her north between the crowds in which case she will get to U3, where she will be close enough to at least feel the fight. 

It will involve an athletics check (you have advantage from raging), if you get over DC15 you do it and look cool; DC10 to DC14 you just do it but land face first in the dirt at U3 (1d4 damage), less than that you end up at U5 face first in the dirt (1d4 damage). Nat 20 will mean you get all the way to grid S3 instead