Doriath vaguely hot take : very few people were actually killed during the second kinslaying (unlike the third)
I've been rereading stuff, and I've come to the conclusion that, contrary to popular opinion, the second kinslaying was not a massacre of epic proportions, with many civilian victims, but an episode on a much smaller scale, unlike the massacre in Sirion.
For the following reasons :
I. Any description/allusion to Doriath in the text focuses on Dior as the (almost) only victim of the third kinslaying :
"But Dior returned no answer to the sons of Fëanor ; and Celegorm stirred up his brothers to prepare an assault upon Doriath. They came at unawares in the middle of winter, and fought with Dior in the Thousand Caves ; and so befell the second slaying of Elf by Elf. There fell Celegorm by Dior's hand, and there fell Curufin, and dark Caranthir ; but Dior was slain also, and Nimloth his wife, and the cruel servants of Celegorm seized his young sons and left them to starve in the forest."
That's the main description of the second kinslaying we have, and Dior and his wife are the only direct victims mentioned (on the non-Fëanorian side).
Later on we read this about the Silmaril in Sirion : "Then Elwig and the people of Sirion would not yield the jewel which Beren had worn and Lúthien had worn, and for which Dior the fair was slain (...)"
Again, no mention is made of any victim but Dior (Nimloth is completely forgotten there).
And finally, in the third mention we have of the second kinslaying : "But Eonwë answered that the right to the work of their father, which the sons of Fëanor formerly possessed, had now perished, because of their many and merciless deeds, being blinded by their oath, and most of all because of their slaying of Dior and the assault upon the Havens."
Again, the only mentioned victim is Dior, and there is no indication of further victims. Now, it could be a bias of our sources, who do favour the famous and high-born (and ignore for example armed guards that could have been there), and also Melian/Elwing's line.
II. That would make sense if we consider that Doriath was at the time of the second kinslaying recovering from an episode of violence on a, I would argue, much bigger scale :
After Thingol was killed, many people were killed in the fighting between the Dwarves and Elves in the caves of Menegroth ("For there was battle in the Thousand Caves, and many Elves and Dwarves were slain (...). But the Dwarves were victorious, and the halls of Thingol were ransacked and plundered").
Probably, crucially, the majority of these victims were the few warriors that they had. Others were probably killed as well fighting the dwarves later on with Beren and Dior, to avenge Thingol and recover his treasure.
So at the time of the second kinslaying, Dior might have had a few armed guards around him, but the impression we get is that he fights the Sons of Fëanor alone, and I would venture that his wife is killed when she tries to come and defend him.
The rest of the population of Doriath would be non-combatants who just flee, probably like they just fled the first time.
And that's why the text says that "a remnant of the people fled" from Doriath : it's not "a remnant" because the Fëanorians killed them all, it's "a remnant" because they were already what was left of Doriath at the time of their attack.
III.It would also explain why during the third kinslaying some of the people of the sons of Fëanor turn against them, but not during Doriath.
"For the sons of Fëanor that yet lived came down suddenly upon the exiles of Gondolin and the remnant of Doriath, and destroyed them. In that battle some of their people stood aside, and some few rebelled and were slain upon the other part aiding Elwing against their own lords (...)"
We are told that Sirion is : "the last and cruellest of the slayings of Elf by Elf ; and that was the third of the great wrongs achieved by the accursed oath". Sirion is a massacre on a large scale, unlike Doriath.
It would also explain why the third kinslaying is referred to in collective terms, not by singling out one individual. Eonwë talks about "the assault upon the Havens."
IV.I think the reason for the difference in terms of scale of violence between Doriath and Sirion is a strict reading of the Oath :
As a reminder, that's the text of the oath in the Silm : "They swore an oath which none shall break, and none should take (...) vowing to pursue with vengeance and hatred to the ends of the World Vala, Demon, Elf or Man as yet unborn, or any creature, great or small, good or evil, that time should bring forth unto the end of days, whoso should hold or take or keep a Silmaril from their possession."
In Doriath, the Sons of Fëanor ask Dior to return the Silmaril. Dior refuses, Dior is slain.
In Sirion however, it's not just Elwing that refuses to return the Silmaril : it's Elwing "and the people of Sirion". The people of Sirion, collectively, therefore fall under the "vengeance and hatred" of the Sons of Fëanor. And that's why the massacre is on a bigger scale, and some of the Sons of Fëanor's people chose to turn against their lords.
V.It would finally make sense in terms of the gradual descent into violence of the Sons of Fëanor
Time and again, we see them (or at least Maedhros) try and keep the violence to a minimum. He (they) try diplomatic solutions, try and ignore the oath, but "the oath of the sons of Fëanor was waked again from sleep. (...)".
There is a graduation in the violence : first the massacre at Alqualondë, which is not premeditated, then the slaying of Dior and his wife over the Silmaril, then finally the attack over the population of Sirion and, later on, the attack against the guards of the host of the Valar.
