(Can you place Nolla a bit off the raft but not too far from the others?  I cannot view the map, so will need to go by descriptions when available.)

(You got it. I will continue with descriptions. The map was, honestly more for me :) I'm afraid with this many players I may get lost figuring out who's where)

(Bree would be at the back of the raft nearer to Pormas.)

(Busy weekend. Finally had warm sunny days after a weeks of rain. I was out foraging for morels all weekend. Got almost 3 lbs :)

Boriglar calls out but there's no visible change in the progress of the invisible things. He the himself turns invisible.

Nolla cast bless so she, Corin and Roardaar get the extra 1d4

Corin readies an attack with arrow nocked. 

Pormas panics and jumps into the river off the back of the boat.

(Enemy actions coming in a bit)

The invisible creatures keep moving forward putting them now about 30' from the raft.

The wyvern and rider start circling staying on average 100' from the raft. The rider raises his arms and a column of rock hard hail starts falling on the party in a 20' radius from the edge of the raft. 

DC14 Dex save for half of 5 bludgeoning and  11 cold damage.

The area of effect is difficult terrain until the end of his next turn with hail creating a layer of ice almost instantly.

(If anyone has skills or reactions that help let me know. edit - wow that damage was shite :/)

That puts the action on Perdot

Nolla dex save: 28

With evasion she takes no damage.

 Boriglar Dex Dave with evasion- 18

 Corin dex save: 4

He curses under his breath for holding his shot and takes aim at the rider longbow attack: 18  damage: 10

He would also like to bonus action Rage

((Dex save 20))

Seeing something moving towards them, but not seeing what it is that is moving towards them, Perdot will try to make them visible by casting Faerie Fire ((Dex DC 16)) over both of them. He then starts to move, but stops and stays where he is, not wanting to be the closest to whatever may appear.

(DEX Save - 23)

DEX save for Wellby - 8

Bree will cast Hunter's Mark on the wyvern as a bonus action and then loose two arrows at it as her attacks.

Attack 1: 22 Damage: 9 plus Hunter's Mark 1

Attack 2: 22 Damage: 5 plus Hunter's Mark 4

For his turn, Wellby will move in front of Bree on the raft facing the invisible creatures to provide her with some cover.

Boriglar pops back into existence and is kind of struggling what to do.  He tosses Two darts at each of the invisible things hoping to hit something while moving in their direction, taking a defensive pose.

Action: 

Dart Attack: 16 Damage: 6

Dart Attack: 11 Damage: 6

Bonus action: patient defense.

Dex Save: 18 (+ cold resistance)

Roardaar moves 20' toward the unknown creatures and readies an attack against any enemy that comes close.

Attack: 28 Damage: 13

(In case he has advantage from Perdot's spell: 16)

Edit: Damage taken = 3 bludgeon + 2 cold

Dex save for Faerie fire: 3

Perdot's casting surrounds the 2 creatures in light. The shapes it outlines are recognizable as trolls.

Bree is able to dodge some of the hail but Welby takes the full brunt if the damage.

(Bree to confirm you're attacking the wvyvern, not the rider?)

Advantage rolls for Bree: 17 13

Advantage rolls for Boriglar: 28 89

Resolution coming below

Bree marks the wyvern and sinks 2 arrows into it for 19 dmg

Boriglar sends out 2 darts the first one is a crit, the second misses the troll. Causing 8 dmg.

Roardaar moves to 10' from the trolls and readies his attack for when they close in.

That brings us to Nolla then Corin 

Nolla moves in to the attack. She casts hex on one of the trolls. She then casts green flame blade on the attack.

To hit: 15

Damage: 5 and 6 fire and 6 necrotic.

If it hit sit does 8 fire to the troll next to it.

Corin will send 2 more arrows at the rider

Arrow 1: 8 + bless: 2  damage: 4

Arrow 2: 14  + bless: 1  damage:9

Nolla re-ups bless and both of Corin's arrows hit causing 11 dmg.

The trolls split up and attack Perdot and Nolla with their claws and bites.

On Perdot:

Bite Attack: 8 Damage: 5 (piercing)

Claw Attack: 26 Damage: 11 (slashing)

Claw Attack: 27 Damage: 12 (slashing)

On Nolla:

Bite Attack: 8 Damage: 10 (piercing)

Claw Attack: 8 Damage: 14 (slashing)

Claw Attack: 11 Damage: 8 (slashing)

The Rider still circling on the wyvern points his finger as a bright streak lances down at the party and erupts into flame. The fireball engulfs everyone in the party as well as the troll engaged with Perdot.

Spell Damage: 22 Dex 14 save for half

Troll 1 save: 21 

The troll does not save and takes the full brunt of the spell as he lets out a hideous wail.

Corin Dex save: 18 plus bless: 2

 Perdot, dodging and blocking the attacks from the troll attempts to also dodge out of the way of the massive fireball, and now regrets staying on the raft... ((Dex save: 6)) ... as he takes the full blast of fire singeing his hair and armor a bit.

 edit: ((forgot)) con save 16 (DC 11) - ((thank the gods, concentration on FF remains))

Dex save : 25