His head may be spinning, but Ghurr manages to shake off the effects of the scream and resist the effect of the song, as does Illithir.

Heran and Faera, however... Your arms drop to your sides, your weapons hang limply. You must get to the mother Harpy at all costs. You start to walk...

You are Charmed and Incapacitated. On your turns you must move your speed towards the Harpy Matriarch by the most direct route. You may reroll your WIS save at the end of each turn, and if your movement would take you into life-threatening danger such as, I don't know, walking off the edge of a tower 1000 ft above the sea.

Thurodim and Mala, you hear nothing, all is silence, but you see the effect on the others, as Illithir and Ghurr shake their heads and focus their wills, while Heran and Faera take their first steps forward, Heran out from the stairwell, Faera already on the roof moving towards the parapet.

The Harpy Matriarch grins a wicked grin as she sings, seeing that she has caught some little mice in her trap.

Illithir, your turn. You have resisted the song of the Harpy. What next?

Here's where we're at:

Danger. It was the ever-present element of his line of work. The very reason why people even hired him. It was something Ilithir had grown accustomed to noticing in the little details. When Thurodin drew his great axe, the elf knew battle had started and swift as the wind moved through the stairs. At the sigh of the harpies, he decided to strike the furthest away, for in his experience it was unlikely that any of his companions could attack from a longer range than himself.

His silver eyes glowed and he released two crackling rays of argent energy. Both hit they mark and despite failing to kill the harpy made her weak and easy to bring down, a feat Mala achieved effortlessly but not before the largest one started to sing. For a moment, a brief moment, he could not help but to few enthralled. How refined and delicate the monster’s song was. Each note perfectly chanted and with an eloquence that spoke of beauty without even using words. It was intoxicating and inspired the truest desire to get closer, to hear better, to hear more. Harpy! He said with the voice of his mind, shaking his head, seeing the creature for what it was. Now the caster knew how so many sailor were enticed to their deaths.

“Who sent you?” Ilithir shouted to the matriarch. Her swarm attacking so suddenly was strange enough, but she mentioned a trap. That made the elf believe she was told by someone that her assault would find no resistance and instead she found an extermination ground. He did not expect and answer, instead casting his eyes upon the hurt enemy. Whispering arcane words he advanced diagonally at full speed and cast another Eldritch Blast.  

Notes: Illithir moves 30ft diagonally in Faera's direction, passing her. He then casts Eldritch Blast on the hurt harpy. In case the first blast kills the creature, the second would then target the unhurt harpy (not the matriarch).

Eldritch Blast 1

Attack: 22
Damage: 6

Eldritch Blast 2

Attack: 25
Damage: 12

The Harpy's devastating injuries make her flight laboured and unpredictable, and she drops a few inches in the air, just enough for the first beam of Illithir's Eldritch Blast to miss her by a hair. The second beam, however, strikes true, and she plummets down, down, down towards the crashing waves far below. 

Illithir expects no answer to his question, and he receives none. Whether she even heard you or not, she simply continues singing, luring Heran and Faera ever closer.

Thurodim, your turn.

Hearing nothing due to the cheese stuffed in his ears, Thurodim still notices Faera moving as if in trance towards the Harpy Matriarch. He has seen this happen before, sailors tragically walking willingly to their death. With desperate strides he takes Skullcleaver in one hand and grabs Faera, trying to tackle her to the ground, anything to stop her from continuing towards her doom.

Grapple (?) Athletics: 27 Another roll if advantage due to rage: 16

He then turns to the Harpy Matriach and let's out a mighty roar.

Faera seems completely unaware of Thurodim's approach, and puts up no resistance as he tackles her to the floor. Her eyes remain turned towards the singing Harpy, and her legs move almost mechanically, mindlessly, as if she were still walking. 

The Harpy Mother scowls at you, though whether she is reacting to the roar or to the fact that you have prevent Faera from falling to her doom, you cannot say. Nevertheless, she continues singing.

Faera, it's your turn. You cannot take any Actions or Reactions, and your only goal is to reach the Harpy Mother, though you are currently pinned down by Thurodim. If there is anything you would like to do which you are able to do, please go ahead, and at the end of your turn make another WIS saving throw.

Must get to the Harpy Mother... must get... being pinned down, she just lays there moving her legs.

WIS save 6

Faera, the spell is broken! You come back to your senses, realising what must have happened, and what might have been...

There is also a great weight pinning you to the ground which you quickly realise is Thurodim, roaring.

Mala, your turn. One Harpy and her Matriarch left, a little way out from the edge of the tower, and Heran beginning to exit the stairwell, a blank look on her face, her bow hanging loosely in her hand.

Mala considers for a brief moment as the pale-blue-skinned woman blankly walks from the stairs.  She had a ways to go to be at risk of nearing the edge, so she makes the decision to focus on attack. 

She calls out a few mystic words to mark the matriarch. (Bonus Action - Hunter's Mark) Then she looses two more arrows, this time aimed at the elder harpy.

(Longbow Attack: 10 Damage: 7 + 3)

(Longbow Attack: 14 Damage: 12 + 6)

If one shot hits, she will use Favored Foe to also mark the harpy. (1 damage)

Supremely pragmatic, Mala assesses the situation and focuses her efforts on taking down the singing Matriarch. 

Her arrows pierce the air, two and a half foot of ash wood with wickedly barbed heads. They also pierce the mother Harpy, who sharply draws in breath, but continues singing as melodiously as ever.

Ghurr, your turn, what will you do? 

Ghurr takes one step towards the harpy's, reaching for one of the javelins at his back. But he stops when he sees how far away the creatures are from the tower. Ghurr may not be a master of words and knowledge, but he knows how strong his arms and legs are. Despite his strength, a javelin at that distance is not a reliable weapon.

Instead he looks around to see what shape the others are in. When he spots Heran making her way to the edge of the tower, a blank, mesmerized look on his face, he realizes what the harpy's song was doing.

He moves quickly to Heran, shouting as he does "Stop listening to bad harpy."

 Ghurr then grabs hold of Heran, restraining her from walking any further from the edge.

Strength/Grapple (Athletics) if needed (with advantage because of Heran's state?): 20  

Ghurr grabs Heran clean off the ground, holding her in a (bug)bear hug to his chest. Like Faera, she doesn't resist, simply continues her walking motion as if she is still moving towards the harpies.

Heran, chances are there isn't much you can do right now, but if you can think of something then please do give it a go, and at the end of your turn make one more WIS saving throw.

Heran would start to walk towards the Matriarch, wondering why she had just tried shooting it, before getting picked up by Ghurr. Her legs just continue to move like she is still on the ground uninhibited.

((Not really much that she can do with the effects, so will just make the wisdom save!))

Heran's Wisdom Save: 16

Both her prizes snatched from her! With Heran and Faera prevented from moving, the Harpy Matriarch stops singing, a snarl across her lips now. As soon as the singing ends, Heran you are no longer affected - you blink and find yourself lifted off the ground, held in big, strong, hairy arms. 

The mother Harpy flies flanked by her one remaining daughter, and as she passes by the tower and away to the east along the coast, Faera, Thurodim and Illithir feel one last taste of her power.

You find yourselves in a vision - you are in the midst of achieving your deepest, most heartfelt desire. It feels so real, realer than your most lucid dream, more real than reality. And it would be so wonderful to stay...

I need the three of you to make another WIS saving throw.

Thurodim WIS save: 5

Ilithir's Wisdom Save: 7

Faeras WIS save 7

Whatever the vision shows you all, it is so beguiling that you find it impossible to shake free. You are Paralyzed until the end of your next turn.

Combat-wise, this doesn't mean much, because as the Harpy Matriarch and her daughter wheel away down the coast, combat is over. But rather than resisting the vision, you give in to it for just long enough, only to find it snatched away from you. You wake up back in a world where whatever you were achieving, you have yet to achieve. 

Now that the screeching and screaming and, most of all, the singing have ceased, you all hear another sound on the rooftop with you, and you realise it has been there the entire time, behind the raucous Harpies. It is the Harpy song, or something very like it, but you feel no effect, it doesn't carry the charm of the one you just experienced. 

Thuridim's deepest and most heartfelt desires...

When the harpy's fly off, Ghurr looks at Heran, focusing on her eyes. When he sees the trance-like draw of the harpy song fade away, he puts Heran back down and pats the rogue on the shoulder.

"Next time not listening bad harpy," Ghurr says.

He then quickly moves to the wounded soldiers. If any are unconscious but can be saved, he will use 'Lay On Hands' to revive them to 1HP.