yeah on second thought, i highly doubt galadriel would have asked them for help unless it was literal right-that-second do-or-die, and honestly maybe not even then. also lol at the last part: the feanorians, furious and feeling betrayed that galadriel... decided to distance herself from them after they stole from and slaughtered her family and people on her mother's side. don't get me wrong, it's a level of unreasonable i'd fully expect them to be capable of, especially from the ones like celegorm, caranthir, and curufin. (caranthir considering his dismissal of thingol -- and you're right, thingol was finwe's best friend, he should reasonably have heard good things about him or at the very least know he's no pushover. and yet ÂŻ\_(ă)_/ÂŻ. celegorm and curufin definitely, considering thingol's understandable refusal to surrender the silmaril made them as angry as it did.) maedhros and maglor are, i do think, less ludicrous, but i doubt they would have approved either, if they knew about it.
also! i just remembered that in nome there's this quote:
Even after the merciless assault upon the Teleri and the rape of their ships, though she fought fiercely against FĂŤanor in defence of her motherâs kin, she did not turn back. Her pride was unwilling to return, a defeated suppliant for pardon; but now she burned with desire to follow FĂŤanor with her anger to whatever lands he might come, and to thwart him in all ways that she could.
this seems to heavily imply that galadriel fought against the noldor in the kinslaying of alqualonde, or at least stood in very obvious opposition to feanor in some other major way. so if we go by this version she'd probably have an even worse relationship with the sons of feanor, to the point that most of them legitimately might not even consider her family (even in that loosest "we're descendants of finwe" sense) anymore.
regarding the time frame of celeborn and galaadriel's marriage: according to the silm at least, they were definitely romantically involved by the fairly early first age, as celeborn is part of her incentive to stay in doriath when finrod departs doriath for nargothrond. nothing about marriage at that particular time, but by the time of thingol's death, they are definitively married:
At that time Beren and LĂşthien yet dwelt in Tol Galen, the Green Isle, in the River Adurant, southernmost of the streams that falling from Ered Lindon flowed down to join with Gelion; and their son Dior EluchĂl had to wife Nimloth, kinswoman of Celeborn, prince of Doriath, who was wedded to the Lady Galadriel.
so they did marry in the first age, and not super super late during it either; all seven sons of feanor were alive and more or less active at the time. of course though the question still remains if they would be aware of the marriage. i'm pretty sure galadriel would have heard about how celegorm and curufin ousted finrod from somebody in nargothrond, which may have soured relations even further, so she'd definitely have no reason to be keeping up communication or telling them about her marital status. and given the feanorians' status roughly around the time (militarily active holding the siege against morgoth, then scattered following the nirnaeth arnoediad), i don't think communication with their very estranged cousin would have been a priority. that said, it's still possible that some news reached their ears, if only through hearsay