(Yeah unless it is a crossbow then you need the Crossbow Expert Feat to be able to attack more then once. As for the advantage I think with Guiding bolt it is only for the next attack so I believe it would only be for the first attack.)

(@Darth, thanks. Just wanted to make sure.)

Kazri nocks another arrow and targets the same Yeti again.

Oathbow Attack2: 9 Damage: 6

(If second attack is with advantage Attack2 9, and also if it deals extra damage 14 piercing damage)

6

With another streak of light the leftmost Yeti tumbles down the cliff face and falls dead. Rhogar then slams the ball of light into the next yeti in line.

Kazri calls an oath on a yeti and strike with her first arrow but the second misses.  Chill makes a solid hit on the far right yeti and Rekuburk leaps forward as the wall of flame drops and cuts one yeti down and then turns and strikes out at the one that Chill hit.

The Yeti on the cliff throws a chunk of ice at Rekuburk

Attack: 14 Damage: 11 bludgeoning damage.

and the other slashes at him with its claws

Attack: 22 Damage: 6 slashing + 3 cold

Attack: 8 Damage: 7 slashing + 3 cold

The chunk of ice misses and only 1 claw attack hits.

 Krom and full order back up

Chill (51/51+10), Rekuburk (79/93), Yeti, Krom (75/75+10), Rhogar (55/55), Kazri (74/76)

Krom scans the area calculating mentally the distance from both yeti. He then nods to himself and starts walking towards the yeti engaged in combat with Rekuberk. As he walks Krom puts back his war hammer into the belt harness and pulls out an hand axe. "This is far enough" says to himself as he takes aim and throws the axe at the yeti. As the axe flies in the air, flames erupt the blade.

Movement: 25ft NE in order to be within 20ft from the yeti on the left

Action: Handaxe Attack: 13 Damage: 6

Extra Fire damage if the attack hits the yeti: 4

The axe spins through the air and strikes the yeti between the eyes and it drops dead.

Despite the somewhat ease the party had in dealing with the Yetis, Rhogar looked around with baited breath, fully expecting to hear the trundling of heavy footsteps or possibly worse in the wake of the fight. Only when nothing comes of it after a tense few moments of silence would a sigh of relief escape his maw, and with but a thought, the miniature sun is dismissed from existence.

"Well done, Master Krom. That wall of fire was perfect, all things considered. Had those bestial cretins had their way, we might've been far more quickly overwhelmed in this fight. Something we can hardly afford, to say the least." Rhogar admitted with a faint bit of mirth to his voice. "Lady Kazri. Rekuberk. How fair you two? Do you require healing? Oli? You good?" As requests are being made and Rhogar rejoined the group, a shivering Gorrah zipped over and back into the hood of the dragonborn.

"Oli and I are fine. Thank you for your concern Mr. Nimbatuul. Yes, indeed master Krom, that was a great idea to keep those creatures at bay." With that said, Kazri looks at the bow in her hand. "It has been a long while since I wielded one of these. Perhaps, I will find more opportunity to use it." She puts the bow away, picks back up her shield, and readies her sword. She then pats Oli on his back. "You did a good job standing firm Oli. I am sure we will encounter more of those creatures here." Kazri looks around. "Do you smell more of those creatures around?"

Oli Perception for more Yetis: 21

Kazri will target the last Yeti with her bow (regular attack).

Oathbow Attack1: 18 Damage: 5

Oathbow Attack2: 13 Damage: 4

One Yeti to go as Chill focuses his attack and lets a bolt fly

Attack: 24 Damage: 29

Stealth to hide 25

Rhogar's hopefully last action prior to the speaking here.

Bonus Action: Ram Sphere into Yeti, inflicting 9 Fire damage. Dex Save(DC 15) for half damage.

Action: Cast Force of Will at Yeti.
Beam #1 -  Attack: 18 Damage: 8 of Force.
Beam #2 - Attack: 20 Damage: 5 of Force.

Between the blasts from Rhogar, the arrows of Kazri and the bolt of Chill the last Yeti falls dead.  As its body slumps to the ground a howl that can be heard across the island chills you to the bone.  It sounded like a Yeti, but more fearsome and terrible.  You cannot determine which direction the sound comes from but you fear you have awakened or angered something on this island.

"... Either way, it sounds as if we might have our work cut out for us." Rhogar admits, voice trembling ever so much towards the end. As if realizing this after, the Dragonborn growled and clenched his hand into a tight fist at his side. "But we must proceed all the same. Even if it must be through whatever creature made that sound just now.... Unless the rest of you would prefer to hunt it down, least it take us unaware at an inopportune time?"

Krom recovers his axe from the dead yeti and as he attaches to his belt one again replies to Rhogar and Kazri with a big smile "An old dwarven proverb says, when outnumbered divide your foes. These Yeti choose to fight the wrong group of adventurers."

As he hears the howl, the dwarf says "I do not like the sound of that." he turns his head looking around unable to find the origin of the sound. "I agree with Rhogar, we must proceed and proceed with caution as we are deep into hostile terrain. The sooner we find the Codicil, the better."

Krom adjusting his gear as he prepares to continue the march towards the Frostmaiden's fortress walks by Rekuberk examining his wounds. "Better to take care of those now lad, we may have to face stronger foes soon." The dwarf chants an hymn of evocation (Cure wounds) placing his hand on the half-orc's arm.
Krom then touches his Holy symbol murmuring a prayer.

( Cure Wounds at 2nd level on Rekuberk 11 - I will then use Harness Divine Power to regain the spell slot)

Kazri can sense Oli's fur go stiff, and she pats the owlbear on his side. "Easy Oli, stay close to me." "I do not like the sound of that either gentlemen." She says to her companions. "I will try to keep my eye on Chill as he scouts ahead."

(Just a FYI, bc I tend to forget that too. If one is withing 10 ft of Kazri, they add +3 to their saves, and are resistant to spell damage. I am going to assume that the Yeti's Chilling Gaze is not a spell damage.

Aura of Protection - While you are conscious, you grant all friendly creatures (including you) within 10 ft. a +3 bonus to all saving throws.
Aura of Warding - You and friendly creatures within 10 ft. of you have resistance to damage from spells.)

Chill moves out from behind the tree and approaches the others. 

"I'm not sure I want to hunt whatever made that sound.  It's a big island,  where would we start?   My only suggestion may be to stay here and wait for it to find us.   But I think I'd rather take my chances and try to find the codical as quickly as possible.  I say we keep moving."

Unless there are objections Chill moves back out in front of the others.   He starts up the switchback and continues on the road but this time point about 30 feet ahead of the others. 

"Agreed Chill. I would rather avoid a fight if possible." Kazri replies to Chill.

(Can Kazri ask Oli to use his senses, and give us a early warning if whatever made the sound gets closer to us?)

Rhogar neither voices further complaint or suggestion, but simply moved to follow after Chill, if albeit more on the alert than ever before. Occasionally Gorrah too tries to help keep lookout, only to slip trembling back into the confines of the Dragonborn's hood. When possible on their way, Rhogar at times hangs back just a little to examine the inside of the tunnels; his eyes readily penetrating the darkness at far greater ranges than any of his companions. Yet short of anything catching his attention in these cursory glances, Rhogar remained content to keep relatively in pace following the others.

You continue into the fog, following the road that leads further up the mountain.  Traveling slower, more cautiously and more alert every crack of ice and strange noise draws your attention but nothing emerges from the fog to confront.

About 20 minutes later you see rising before you is a six-hundred-foot-tall mountain of glacial ice, its peak carved to resemble a gigantic skull wearing a crown. Weaving up the mountain’s southern slope are enormous stairs hewn from the ice. These steps, which extend from the base of the mountain to the base of the fortress, were clearly made for giants.

The steps end in front of a double door made from slabs of ice with dragon skulls and bones embedded in them. Carved into the lintel is a single word in the Dwarvish script.

Those who understand the language can read the Dwarvish word carved above the doors which translates to “Grimskalle.” 

As the group approaches the fortress Krom says "It seems that we have reached our destination." The dwarf looks around as he continues "We have to find a way to enter the fortress without alerting the giants."
Krom walks next to Kazri and says "Now it's the perfect timing for granting you a way to understand the language spoken by the Giants." Touching Kazri's forehead Krom chants an hymn of divination (Tongues).
"I still have the strength to channel the power of this hymn one or two times more if necessary."
The dwarf, adjusts his gear and then walks by Chill. "You have keen eyes my friend, I'm sure that if there is another way to enter this fortress, you will find one." Krom chants an hymn of divination (Guidance), enhancing for a brief time the tabaxi's senses.

Chill looks up at the imposing fortress.  If he were alone climbing the walls and finding a way in might be a simple prospect.   But any way they tried to get in short of the front doors would need to be doable by the whole team.   He looked for weaknesses and points of entry that they might reach by climbing.   

Guided by Krom's hymn he looks around. 

Perception 24 + 1