Telepathically: "Alright.  It's time for "I make a distraction and the rest of you run for it".

Ember walks quickly past the elemental to the other side of the hall from our group and says: "Dash Door Delivery Service.  Who ordered the Fast Food?"  

Telepathically: "RUN!"

In the darkness, Kordia's hands suddenly shimmer with a translucent energy which is thrown at plasmoid being...  with a second dagger like shard of energy following right behind the first.

Action - Attack - First Psychic Dagger -> game log ->  To Hit:  21   Dmg:  9     (psychic)

Bonus Action - Second Psychic Dagger  ->  game log ->  To Hit:  Dirty 20       Dmg:  6     (psychic) 

Through the link -- "RUN RUN RUN"  as well as barks at Artan -- "Run.  I will cover you."

Kordia will move to any other shadow available... waiting to see how Flax fares.

As he is sitting right next to it, and now's a perfectly good time to be a little... reckless. Flax picks up the blade resting against the table as he stands. Presumably it belongs to the gnoll, and he may object. Nonetheless, Flax feels having steel in his hands at this moment is worth the kerfuffle it could cause. Mentally, "It is go time ladies and gentlemen, be ready for violence."

(so my wild card plan didn't happen as I was asleep at that time. I will keep it up my sleeve for the next time it might be relevant) 

"If we can all get to the other side of them, I can hold them off!" and Artan turns invisible (Firbolg ability, BA and lasts until the start of his next turn) and runs towards the target door, dashing if required. Knowing he will become visible soon, he makes sure he ends up not next to any of the guards.

(So Ember pops out with sarcasm, Korda blasts from the shadows and Flax granmbs a blade.  They shouldnt see Artan.  Time to add more confusion to the guards.)

"OOooo, I see why you ordered takeout.  Your kitchen is on fire!" (points at the smoking door)

Ember concentrates on the PFG&E spell and tries to run for the door while they're still surprised.

Ember walks out of the tunnel, pretending to be a delivery person. Her puns and sarcasm are lost on the Elemental, who looks flabbergasted at this development.

Kordia summons blades of energy, and sends them flying forwards. They strike the Ooze, and it melts to the ground, the equivalent of doubling over in pain. It's gooey tentacles clutch at the top of its mass, as if holding its head.

Flax decides to go for it, and grabs the Beast's weapon. He hefts the weapon, which is equivalent to a Great-sword. One thing of note: Flax is closest to the table, and the Dryad and the Elemental don't have their weapons. The Ooze has their axe floating inside of them, but Flax could use his item interaction to pick up and throw one of the weapons across the room, making sure the enemy couldn't get it.

Artan turns invisible, and runs across the room.

The four monsters all look very surprised.

Initiative (we'll do it by each character):

Ini5iative 17

(So no reaction to my pointing out the smoking door?)

Sorry, I had to go before I could finish the monsters turns

Beast & Elemental > Kordia, Ember, & Artan > Ooze & Dryad > Beshlog & Flax

Beast's Turn!

The Beast looks surprised as Flax takes his weapon. He snarls, and leaps upon the Leonin, trying to wrest the blade from his hands. I'll roll STR checks for both the Beast and Flax to see who wins

Flax's STR check: 23

Beast's STR check: 11

Flax manages to keep hold of the weapon, but the Beast has leapt upon him, and tries to bite the lion-mans face.

Bite Attack VS. Flax: 10 to hit, 15 Piercing damage and Flax has disadvantage on his next attack roll.

Elemental's turn!

The Elemental dashes to the table, quick as lighting, and just as fast releases two arrows from their bow, which they just grabbed. The arrows shoot through the air at the retreating form of Ember, crackling with electricity

Bow attack #1 VS. Ember: 10 to hit, 9 Piercing damage and 8 Lightning damage

Bow attack #2 VS. Ember: 16 to hit, 10 Piercing damage and 4 Lightning damage

The Dryad turns and looks at the smoke, and suddenly a scared expression creaks over their normally wooden face. Tree no like fire. Or axes.

Kordia, Ember, & Artan, GO!

With Flax engaged with the Beast,  Kordia plans to exploit the Beast's focus on Flax and execute a sneak attack with her psychic daggers.

game log --> first strike with sneak attack ->  To Hit:  21          Dmg:  7  +   Sneak Attack Dmg:  13 ==  20 pts dmg psychic.

                        second strike is 'just' a strike -> To Hit:  10       Dmg:  7 psychic

Kordia tried her best to stealthfully approach for a backstab... and got one solid hit in before the bodies twisted and turned as she attempted her second strike... failing to do more than graze the Beast's thick skin.   

If she has any movement left, Kordia will try to keep the Beast & Flax between herself and all the other monsters.

(for some reason it isn't showing the numbers rolled when I hover my cursor over the hit rolls.  Were the attack rolls made with disadvantage from the PFG&E spell?  Since elementals are one of the affected creatures.)

Ember stops to cast Wither and Bloom at 3rd Level.  She centers it to get as many of the creatures as she can in the area of effect (but especially the Elemental and the Beast), and give the healing to Flax.

11   And spending a sorcery point to re-roll Ones.  Con 14 saves

Quote from Arthuropodd >>...

11   And spending a sorcery point to re-roll Ones.  Con 14 saves

 No ones, so no sorcery spent

"Hey guards!  If the Masters tower burns down, do you still get paid?  Maybe you should put out the fire instead of attacking us."

Flax is uncertain why the beast-man decided to choose violence against him, it must have just been waiting for commotion to lash out. But he gives it a look, one that tells the tale of the beast's coming demise. 

Heals: My HD: 3 plus Ember's modifier: +3

At the start of his turn, Artan becomes visible. Before I fully decide what to do, are any of them wearing metal armour?

None of them are wearing armor. Though if you plan to use fire, keep in mind there is a literal person made from wood in this combat scenario

Kordia sneaks up behind the Beast as it leaps upon Flax, and delivers a solid stab to it. The blade sinks into it's flesh, and it howls in agony, badly wounded

Ember summons the magics of life and death, channeling the power of her gift from the gods, and sends forth a cloud of roiling death which envelops the Beast and the Elemental. But, due to the AOE, Kordia is also affected by the spell and must make the neccessary DC 14 CON save or take 11 Necrotic damage

Artan, Time to act!

CON check 13

HOWEVER, Kordia has a nice little 'special' that may help here >>> Psionic Power: Psi-Bolstered Knack

Psi-Bolstered Knack >>> 7

Which, added to the original [13] == DC save:   20   (and I burn a psi die slot)

Quote from Raccoon_Master >>

...Ember summons the magics of life and death, channeling the power of her gift from the gods, and sends forth a cloud of roiling death which envelops the Beast and the Elemental. But, due to the AOE, Kordia is also affected by the spell and must make the neccessary DC 14 CON save or take 11 Necrotic damage...

 The spell description reads "Each creature OF YOUR CHOICE in that area ..." (caps mine).

Ember didn't chose Kordia.  It's fine if this is how the spell works in your game.  But if so, Ember should have the choice of using a different spell.

I was considering using heat metal if they had armour on, cook them alive by the time they can get armour off (unless it was the ooze who could probably squeeze out much quicker than normal times). But instead Artan will see something of himself in the dryad and immediately see the threat they can be, so activates burn mode. He summons another small mote of starlight and attempts to burn the dryad.

23 to hit, 11 fire damage