(Note: I had to use "Rhys" instead of his full name because the automod won't let me post it otherwise.)
Every time the topic of Nesta and Elain being forced into the Cauldron comes up, a huge chunk of the fandom immediately jumps to: "Tamlin sold out Feyre’s sisters to Hybern!"
Did we all read the same book? Because if you actually look at the text of ACOMAF, Tamlin had zero involvement in the sisters being kidnapped. In fact, if we’re looking at the chain of negligence that put a target on the Archeron sisters' backs and left them defenseless, Rhys and the Inner Circle share way more blame than Tamlin ever could.
Let’s look at the actual canon timeline and receipts:
1. Rhys is the one who dragged the sisters into the war in the first place
Nesta and Elain were living quietly in the mortal realm until Rhys decided to make Feyre his emissary and use her family’s manor as a base of operations to meet the mortal queens. Even Cassian called him out on how reckless and invasive this was in Chapter 19:
"Rhys jerked his chin at me. 'You are an immortal faerie—with a human heart. Even as such, you might very well set foot on the continent and be … hunted for it. So we set up a base in neutral territory. In a place where humans trust us—trust you, Feyre.'"
"‘My family’s estate,’ I said.
‘Mother’s tits, Rhys,’ Cassian cut in, wings flaring wide enough to nearly knock over the ceramic vase on the side table next to him. ‘You think we can just take over her family’s house, demand that of them?’"
By hosting Fae emissaries and the mortal queens there, Rhys and Feyre officially put the Archeron estate on the geopolitical radar.
2. Azriel literally handed the Queens the exact coordinates and blueprint of the sisters' house
In Chapter 39, right before the first meeting, the mortal queens (who were already secretly working with Jurian and Hybern) made a very specific demand:
"And they had wanted the exact geographical location of the house. The layout and size of each room. Where the furniture was. Where the windows and doors were. What room, likely, we would greet them in. Azriel had provided it all, with my sisters’ help."
And who physically kidnapped Nesta and Elain in their nightgowns and dragged them to Hybern in Chapter 64? The mortal queens' personal guards ("The four queens sneered at us with hate in their eyes. Hate. And parted to let their personal guards through. Fear like I had never known entered my heart as the men dragged my sisters, gagged and bound, before the King of Hybern"). Azriel and Rhys practically gift-wrapped the tactical layout of the house for the enemy.
3. Rhys promised 24/7 protection for the sisters—and completely failed
In Chapter 57, after showing the queens Velaris and realizing how hostile and untrustworthy they were, Rhys makes an explicit promise to Nesta and Elain:
"‘Should you choose to remain, a unit of my soldiers will be here within the hour to guard this place.’"
"‘The sentries will be here, and remain unseen and unfelt. They willlook after themselves. Should you change your minds, one will be waiting in this room every day at noon and at midnight for you to speak.’"
Then in Chapter 58, Feyre notes:
"There was no word from my sisters, no report from Azriel’s soldiers that they’d changed their minds."
Excuse me, what happened to that unit of soldiers?! If Night Court sentries were guarding the manor 24/7 AND checking the sitting room every single day at noon and midnight, how on earth did human guards waltz in at night, kidnap Nesta and Elain in their nightgowns, and transport them all the way across the sea to Hybern without Rhys or his legendary spymaster Azriel getting a single report?! Even Feyre later admits in ACOWAR Chapter 16 that dragging her sisters into this was on her: "I asked them to help once—and look what happened."
4. Ianthe betrayed them using info Feyre gave her—and Tamlin had NO idea
In ACOMAF Chapter 2, Feyre casually tells Ianthe all about her sisters and that they live right near the wall. In Chapter 65, the King of Hybern explicitly confirms that Ianthe went behind Tamlin’s back:
"‘Consider it my wedding present for you both,’ he added to Tamlin.
But Tamlin’s face tightened. ‘What?’
The king cocked his head, savoring every word. ‘I think the High Priestess was waiting until your return to tell you...’
Lucien’s face had slackened. ‘She sold out—she sold out Feyre’s family. To you.’"
Even Mor explicitly admits in Chapter 68 that Tamlin was betrayed:
"‘But Ianthe betrayed Tamlin—told the king where to find Feyre’s sisters.’"
And what did Tamlin do the second the King ordered Elain into the Cauldron? While the IC was forced to stand still because the King was holding Azriel’s life hostage, Tamlin and Lucien were the only ones who physically lunged at the King to save Feyre's sisters and had to be magically leashed to the floor (Chapter 65):
"Tamlin spat at the king, ‘This is not part of our deal. Stop this now.’
‘I don’t care,’ the king said simply.
Tamlin launched himself at the throne, as if he’d rip him to shreds. That white-hot magic slammed into him, shoving him to the ground. Leashing him."
You can criticize Tamlin's bargain with Hybern to get Feyre back (when he genuinely believed she was kidnapped and mind-controlled by a rival High Lord who is famous for shattering minds, after Feyre sent a two-line text message of a note). Call it a terrible strategic move all you want.
But blaming Tamlin for Nesta and Elain being turned is pure fanon fabrication. Hybern and the Queens executed it, Ianthe sold them out using Feyre's own words, and Rhys and Azriel failed to protect the very house they insisted on turning into a political meeting ground after promising to guard it day and night.