ok so ignoring for a bit that im really out of it (and thereby not the most coherent), all im going to say is that the silmarillion fandom REALLY needs to learn more mediæval history. and im not meaning the military stuff, not really. im meaning the cultural details that were very much something that tolkien was aware of (and incorporated into his texts).
taking children as hostages (whilst not really a moral thing, but this isnt about the morality of any of it) was not done for the same reasons necessarily as it is today. hostages were often means of guaranteeing non-aggression (or alliances, or tribute) between two nations, or of fostering good relations between the two by having one of their children be raised amongst another culture. on that last note, that was often done as a means of ensuring (vaguely) successful marriages, such as how sigismund, hre, was raised in the hungarian court & culture, to ensure the success of his marriage to mary of hungary (this was quite convenient as he later became king of hungary de jure uxoris but thats not rlly relevant). whilst somewhat different to hostile hostage-taking, fostering has also been very common throughout history, and even happened cross-class in some places (like ireland, where iirc the eldest sons of irish rulers were often fostered with common families, so as to increase the phenomenon known as "compassion"; though tolkien took little, if any inspiration from irish history, and most parallels found are from the welsh & the norse often having similar customs and/or mythologies to the irish).
holding nobles to ransom was afaik mostly done to adults, usually hostile knights, after the advent of chivalry in europe.
the point is, children were not held to ransom, and it does not once state that the sons of fëanor ever held elrond & elros to ransom. they were hostages, likely as some means of discouraging gil-galad from pursuing military action (though lets be real, gil-galad likely lacked communications w/ the sons of fëanor at that point, given the whole "morgoth controlling all the land" thing), but mostly because it was What Was Done with prisoners of war that were children. this would've meant that e&e were treated well, as they were wards of the house of fëanor (as this is what hostages were), and would've genuinely been treated almost as well, if not just as well, as maedhros & maglor's own sons (not that they had any but yknow). it makes sense in the context of this that "love grew between them", as this quite frequently happened in such situations, even when the hostages were more poorly treated (see: james i of scotland & his relationships with henry iv & henry v of england, and how his loyalty to his kidnappers [this was a kidnapping situation, not a legal example] eventually resulted in the scottish nobility murdering him bc he fought against scottish soldiers on the behalf of the english, in france).
furthermore, the sons of fëanor had zero reason to hold them to ransom. gil-galad & círdan likely lacked the resources to care for their own people, let alone the fëanorian host (which likely was larger at this point than is implied, as the text itself only ever seems to mention the soldiers, and even were the fëanorians a roving military band, they would've had huge numbers of camp followers, both by necessity, and bc any sane elf/man/dwarf in late-stage beleriand would be hanging out with the biggest army they could find). and whilst it's uncertain if they knew that elwing was alive (and they wouldve known next to nothing abt eärendil), what they did know was that she 1) had previously refused to negotiate for the silmaril, and 2) if she were alive (this suspicion only being possible bc let's be real, a river delta does not have deep water; they wouldve found her body quite easily), she almost certainly was too far away for them to communicate with at all. also, if she were dead, they couldn't negotiate with her. on account of her being dead. the sons of fëanor wanted the silmarilli, and elrond & elros were not a viable means of getting any; and they were not stupid enough to think that they would have been. also, again, the text never once states that they were held to ransom.
uhhh tl;dr: hostage did not mean the same thing in mediæval times as it does today, precisely, and it is never stated that elrond & elros were ever held to ransom. they were wards of the sons of fëanor, albeit illegally acquired wards.
