Barmo takes an involuntary step back as he sets his eyes on the massive rats. With a slight shake but building confidence he swings his sling and lets loose a rock at the lead rat.

Sling Attack: 14 Bludgeon Damage: 6

Barmo lets fly and pegs the first rat coming out and knocking him good. It's very hurt, but other continue to swarm past him.

That brings us to Ed

 Ed will produce flame at the nearest rat attack: 9  damage: 4

Can we tell how many are coming at us? 

You still don't know how many are coming out. There are 4 that are outside of the boat now and you can see at least 4 more behind them trying to squeeze through.

Esmee fires her readied arrow at one of the rats streaming from the open hull. Attack: 28 Damage: 8

[Horde Breaker: Once on each of your turns when you make a weapon attack, you can make another attack with the same weapon against a different creature that is within 5 ft. of the original target and within range of your weapon.]

Immediately after loosing the first arrow, she smoothly draws and fires a second at another rat climbing around the first. Attack: 15 Damage: 5

Nice Crit! Both of those attacks hit and the crit kills R2! With the second attack badly injuring the next.

So we have R1 badbly hurt, R2 Dead, R3 badly hurt

Eikis takes aim at one of the still-struggling rats and exhales, firing a crossbow bolt at it:

Attack: 16 Damage: 8 piercing

(As a bonus action,) She orders Vicious to attack the other injured rat:

Force-Empowered Rend Attack: 14 Damage: 8 force

Eikis and Vicious easily dispatch the two injured rats. 

The one uninjured rat from that group seeing danger both ahead and behind turns and starts swimming down river in an attempt to flee.

15  1  1  5  1  13 

Two other rats follow and start swimming down river also. Leaving four who make it to the shore. Two of those four try to dash for the safety of the hills, paying little attention to the party.  The last two don't have the movement speed to get further than a couple feet onto the shore as they both seems to be headed in Barmos direction. From what you can see, all the rats are now out of the ship. (They are not able to attack this round after swimming ate up much of their movement)

Eikis fires again at one of the four rats that are heading towards Barmo:

Attack: 25 Damage: 9

Vicious will ready an action to rend the first rat within Barmo's range, while staying close to Barmo to defend him:

Attack: 16 Damage: 6

Esmee shoots an arrow at the second rat. Attack: 9 Damage: 10

edit: Lucky reroll of the 1 for attack 15

Ed seeing his fire not doing much gets frustrated and spends his action wildshaping into a Panther.

Seeing the last of the giant rats scurrying in his direction Barmo sets his stance with his buckler at the ready and winds up for one last sling.

Sling Attack: 10 Bludgeon Damage: 5

Here's how I'm going to distribute damage to maximize attacks. Esmee easily has the range to attack one rat fleeing into the hills and neatly slots an arrow into the back of the rats head as it's fleeing Killing it. 

Barmo squares up and let's loose his sling Killing one of the rats headed in his direction.

While Eikis's attack misses, Vicious is successful and Kills the last of the rats headed toward Barmo. 

That takes care of the rats in melee and leaves one fleeing into the woods and three swimming down river.

At this point we can drop out of initiative. You can choose to chase and kill the fleeing rats but I don't think we have to do attack rolls. Ed as a panther would have no problem catching the rat fleeing into the hills and jogging down river, if you even had to, to keep the other rats in range while you picked them off wouldn't be an issue.

Though a wave of the wigglies washes over Barmo as Ed changed into a panther, the large halfling reassured himself it was the path his good friend choose in life.

"Ed, try and take that one in the forest if you want but I say we dive into this wreck. There could be some interesting things!"

Being Ed cant communicate with his friends while in animal form he will stay with his friends. If they choose to enter the wreck he will try to accompany them.

@DM: is it possible to wade/swim in panther form? 

Yeah, sure. Panthers can swim. It would be half movement like usual. You shouldn't really need to though. People with ranged attacks can pick of the rats in the river easily. 

We can just say everyone spend a minute mopping up the rats and move on. That's fine.

It seems like you all want to check out the ship?

Ed will go with what his friends decide to do

Esmee shoulders her bow after the group has handled all of the rats. She peers up at the wreckage at Barmo's suggestion that they go in and explore and a little shiver runs down her spine. It's super creepy.

Outwardly she simply shrugs, offering no protest.

The party heading to get a better look at the ship head to the fallen mask 'bridge' and make their way up it. Eikis sending Vicious ahead for recon. Not sensing any danger from Vicious everyone makes their way to the deck of the ship. Fortunately you are all light as many places of the deck look almost burnt through and unstable to walk on. The deck is tilted a few degrees but still walk able. There are the remnants of a captains quarters in the rear of the ship. It's been badly burnt and the roof is collapsed in. The other thing you notice it that the main hatch leading below decks has a large padlock on it.

"Ok, so. A locked hatch leading down into the boat that is locked on the outside. Not great," Barmo would bang on the hatch to see if there is a reply though doubting it.