Krom through sheer willpower manages to resist the attempt of the two duergar to influence his mind. "It will take more than your feeble attempts to defeat a Smith of Moradin!" shouts replies in defiance at the duergar attacked him.
The dwarf counterattacks by swinging the warhammer with all his strength in a uppercut movement and at the same time summons a spiritual hammer that immediately mimics Krom's movement.

Action (Attack on the duergar that attacked Krom)
Blessed warhammer Attack: 15 Damage: 9 + 7 of Fire damage due to Divine Strike

Bonus action (Attack on the duergar that attacked Krom)
spiritual weapon Attack: 21 Damage: 7

Dex save 13

Chill whirls around to face the new threat behind him, leaving the others to the rest of the party to deal with.

He again takes steady aim and fires at the new threat.

Attack: 30 Damage: 49

As a Reaction he will use Uncanny Dodge to take half damage from the attack.

Con save 11

Gorrah Dex 15 savaing throw 15 vs 16 fire damage

Concentration saves 9, 7

Gorrah can indeed sense the location of who you presume to be Xardorok.  Vellynne confirms as she screams the he is indeed Xardorok and she really wants you to kill him, or set her free so she can do it herself.

Rhogar directs his attacks towards Xardorok who is able to resist being poisoned by Gorrah.  Xardorok releases a hellish rebuke against Gorrah who is able to dodge half the damage  and takes 8 unless Rhogar chooses to resist that as well, then 4.

Chill is also under attack and though he uncannily dodge some of the hurled firebolts he is still struck by the attacks.

Krom is hacking away at one of the torturers who doesn't look like he can take much more.

The two torturers again turn the hatred onto the dwarf and try and turn him against his friends and also slash at him with their daggers.

The first duergar casts a spell and Krom must succeed on a DC 12 Intelligence saving throw, or the duergar causes it to use its reaction to force Krom to make one weapon attack against Kazri.  It also moves forward and strikes at Krom with a dagger.

Attack: 9 Damage: 6 piercing + 9 psychic

Krom's attack if he fails Attack: 29 Damage: 8

The second does the same and Krom must succeed on a DC 12 Intelligence saving throw, or the duergar causes it to use its reaction to force Krom to make one weapon attack against Kazri.  It also moves forward and strikes at Krom with a dagger.

Attack: 23 Damage: 4 piercing + 11 psychic

Krom's attack if he fails Attack: 11 Damage: 8

Xardorok, being a very vengeful and mean spirited duergar decides that you will not be freeing his prisoner and directs two blasts of eldritch energy at Vellynne as he becomes visible again.

Attack: 23 Damage: 6

Attack: 13 Damage: 7

The pope head also continues to lob fire at Chill

Attack: 16 Damage: 14

Attack: 25 Damage: 25

Vellynne is still alive and concious as she screams curses at Xardorok.

Players back up

(OOC: Rhogar will most certainly halved that damage, and a 12 doesn't beat Gorrah's DC, as her's is the same as Rhogar's spell save DC thanks to a feature. But safe to assume there was a seperate adv. roll elsewhere 'cause Dwarf.)

Rhogar's eyes and Gorrah's scales shimmer with an inner cyan light, protecting the latter from what flames managed yet to coat her form. Immediately after which, Gorrah starts harrying the dwarf by nipping at his face and tugging at his beard, keeping him distracted as the Dragonborn raced to the side of the chair to give it a closer once over.

What started off as a frustrated growl in seeing no key(no surprise there) soon turned into an infectious chuckle, or so Chill and Vellynne despite the circumstances. But while it's easy enough to fight off the urge, something about the sound and tone itself seemed to carry power, as both would feel a surge of vigor return to them. "I'll have her free shortly. Focus on the rest."

Bonus Action(Rhogar): Twinned(-2sp) cast (2nd level)Hlal's Laughter on Chill and Vellynne, restoring 7 HP to both.

Action(Rhogar): Attempt to Break Vellynne's restraints(or at least one of them): 26. (If a flat strength roll would be more appropriate however, subtract 4 from above roll.

OR(If the cuffing mechanism looks too thick to muscle open)

Action(Rhogar): Pour a vial of acid over the cuffs near Vel's hands/arms.

Action(Gorrah): Keep Xardarok Distracted.

Future Reaction(Rhogar): If Gorrah's damaged, Rhogar will burn a reaction to grant her resistance again. If Rhogar is however damaged first, he'll cast Righteous Retribution at 1st level against attacker. Dex Save(DC 16) to take half of 10 Fire Damage.

Kazri realizes that these Duergars are not exactly in the right state of mind, and apparently they are willing to fight to the death. She commands Oli to guard the door. He's to keep the door closed, and attack any of the bad folks that try to open it. She then rushes to Vellynne and heals her as much as she is able (Lay on Hand 45HP max). She checks the shackles to see if she is able to release the prisoner.

Perception: 22

Krom 1st Intelligence save 20
Krom 2nd Intelligence save 11

Krom manages to resist the first spell cast by the duergar, but the second attempt made by the other torturer is successful. Krom swings his war hammer at Kazri, but the dwarf at the last moment regains control of his body crushing his weapon on a tile next to the paladin.

The dwarf turns towards the two torturers "This ends now, you have toyed with me long enough." The spiritual warhammer swings itself down attempting to crush the skull of the wounded torturer while Krom chants an hymn of evocation summoning into the room a score of spectral dwarves that immediately proceed to hack and smash all the duergar within their reach.

Bonus action
spiritual weapon on the wounded torturer Attack: 21 Damage: 5

Action
Spirit guardians cast at 4th level - The group and Vellynne are uneffected.
20 Radiant damage and halved speed to any duergar within 15ft from Krom. Save DC 15 Wis to reduce the damage

It's bolts vs fire as Chill continues to take steady aim and fire at pope head as he uses uncanny dodge to try and avoid the fire as much as possible.

Attack: 27 Damage: 30

Wis saves 14, 9, 5

Kazri tries to determine if she can free Vellynne but a moment later a very tall and very strong Dragonborn steps in and digging his claws on the manacles breaks he free from the the bonds that hold her.  Kazri catches he as she falls free and heals her, nearly all her wounds disappearing. 

Krom slams the spiritual weapon into the first torturer and a moment later as the guardians fly around him they bring the first torturer down.

The remaining torturer stabs at Krom with its dagger, frustrated that any of their efforts to control the dwarf have failed.

Attack: 6 Damage: 7 piercing + 6 psychic

Attack: 10 Damage: 5 piercing + 8 psychic

Xardorok, nearly screaming in his rage continues to try and kill Vellynne

Attack: 16 Damage: 8

Attack: 23 Damage: 14

The pope head also continues to lob trade fire and bolts with Chill

Attack: 8 Damage: 8

Attack: 8 Damage: 6

Players back up

(Is Xardorok visible now? Also, is there anything that Kazri can do to protect Vellynne or take the damage instead?)

Krom, seeing that Rhogar and Kazri have freed Vellynne, focuses his efforts on taking down the torturer slamming on their chest his flaming hammer and then following up with his spiritual hammer. In the meanwhile, the spectral dwarves keep smashing and slashing all the duergar in their reach.

Action 

Warhammer attack on the torturer Attack: 15 Damage: 8　+8 of fire damage 

 Bonus action Spiritual weapon on the torturer Attack: 17 Damage: 10

Spirit guardians recurring damage to all enemies within 15ft of Krom 17　wis 15 

Having had quite enough of Xardarok's vindictive attacks, Rhogar practically roars as he leaps over to try and grapple the dwarf, before forcing him further away Vell. "My axe! Grab it from my belt if you must Vellynne, or find cover." He throws back sharply over the shoulder, before then focusing his thoughts slightly elsewhere. In that moment, Gorrah zips around once more to try and catch duergar king in-between the joints, hopefully incapacitating him for a time. 

Action(Rhogar): Grapple Attempt on Xardarok for 22.

Movement(Rhogar): If Above grapple attempt is successful, shifting Xardarok about so he remains in the spirit guardians but stays out of melee at least with Vellynne.

OR(if not able to get within reach due to lack of room)

Action(Rhogar): Cast (1st level)Divine Breath on Xardarok. 
(Ranged, Lethal)Guiding Bolt - Attack: 19 Damage: 20 of Radiant.

Bonus Action(Rhogar): Command Gorrah to Sting Xardarok.

Action(Gorrah): Stingcinaty on Xaradok.
(Melee, Non-Lethal)String - Attack: 23 Damage: 6 magical piercing damage. 
Con Save(DC 16) or become poisoned for an hour. If save failed by 5 or more, creature is also unconscious while poisoned this way.
(if attack was at adv. from bolt: 9)

"Go to the entrance of the secret passage!!" Kazri points to the place where they came from. Seeing that Rhogar is taking care of Xardorok, she strikes the remaining torturer.

Dragonslayer Attack1: 29 Damage: 7

Dragonslayer Attack2: 13 Damage: 8

Then she will return to guard Vellynne. (She will take the AoO if applicable).

Chill hears the commotion in the room behind him but he can't turn to see what is happening as he has to keep dodging balls of fire flung at him by pope head.  And he is fixed in place so he can keep steady aim and try and finish him off.

Attack: 26 Damage: 25

Same BA, action.  Same Uncanny Dodge reaction if needed.

Reroll a 1 with piercer feat 2