Initiatives: Monster 5, Louisa 1 (Aiden no longer has a sheet so will be a non combatant, he freezes and is rocking back and forth muttering something)

Everyone is up, will do Louisa last just before the monsters. Apart from Kra-osh who might just have time left on divine sense, all anyone else knows is that there are invisible creatures, no locations currently known (Petro is technically first so if he cast fairy fire and reveals any of them, everyone else will see those ones) 

Which he will do, casting so he'll cover about 20-40 ft back from the wagon. faerie fire

And let's go with a lovely shade of chartreuse for the color

On her turn, Ondrea will raise her holy symbol and Bless Petro, Ramos, and Kra-osh.

Kra-osh charges at the strongest looking enemy, then swings at them with his Longsword, using a first level spell slot to use divine smite, if it hits.

Attack: Attack: 8 plus 2 for Bless. Damage: 31 (Edit: They just got obliterated! Also, it should have advantage if they were hit by the faerie fire, so here's the other attack roll: 8, plus 1 for bless)

The 2 behind are in faerie fire (the others would only be if you guys were covered too) so dex saves: 23 14 (DC?)

Kra-osh, you can't see what looks strongest as your sense doesn't show what type of fiend they are, so take your pick at which one you go to. 

Angorn will cast Hunter's mark on the creature he can see and pull out his bow and shoot at the one he can see with sharpshooter.

Attack: 9 Damage: 15

(EDIT: sorry don't know what my jobs internet security has against some of these posts.)

It dies, very much so

Ramos runs towards the remaining visible fiend, going into a rage and striking it (if he can reach it).

BA: Rage, fiend makes DC14 dex saving throw or take 1 lightning damage, half on success

A: Attack! 26 Damage: 14

DC 15

(one fiend passed so no fiends visable yet, do you still rage or wait a turn?) 

Ah, I missed that the one passed the spell, I'll run to the center of the caravan and rage

Louisa will hold her action to hit anything that comes close enough. 

The 4 remaining fiends go, looking at the dead one, and the others as they appear, these are all more imps.

One on Petro (the one who succeeded on the spell): Attack: 22 Damage: 6 (17 or half on DC11 con save)

One on Angorn: Attack: 21 Damage: 5 (14 or half on DC11 con save)

One on Kra-osh: Attack: 20 Damage: 4 (9 or half on DC11 con save)

And one of Ondrea: Attack: 22 Damage: 7 (12 or half on DC11 con save) 

CON save 17

CON save 6

Angorn not seeing his attacker takes significant damage by surprise.

On his turn Angorn will switch the Hunter's Mark (Bonus Action) to the imp attacking him, and shoot with his longbow w/disadvantage because too close.

Attack: 26 Damage: 7 
Hunter's Mark if hit 1

Ondrea staggers from the hard hit, but recovers and raises her holy symbol again to cast Spiritual Weapon.  In tandem, both she and the animated weapon swing at the imp.

Attack Attack: 22 Damage: 8

Spirtual Weapon Attack: 12 Damage: 3

Con save: 8

Petro reels back from the hit, and a little bit pissed now, will cast dissonant whispers on the imp that attacked him, reaching into its mind and whispering things about celestials and whatever else imps don't like. 20 psychic or half on a DC 15 Wis save.

And for an encore, he'll give bardic inspiration (d6) to Angorn.

Ramos runs to intercept the fiend attacking the bard. Assuming that he can get there, he strikes Recklessly with both his aura and his trident.

BA: Storm Aura, DC14 Dex save or take 2Lightning damage

Action: Attack! 26 Damage: 14

(If he can't see the strongest one, he would've just hit one of the invisible ones at random)

Kra-osh charges at another Imp, swinging at it normally with his longsword.

Attack: 18 (+2 Bless? If that’s still active.) Damage: 6

(good point with bless, Ondrea needs to make a concentration check) Kra-osh never took damage, not from it not reaching his AC, but from him killing it while invisible.

Save for the dissonant whispers 12 it dies,

Ramos can go to either Ondrea or Angorns one, Kra osh goes to the other. If Ondrea makes the concentration check then Kra-osh kills the last one, otherwise he misses and one is left