[Maédhros]

keep in mind that Feanor is already tainted by his oath, and has declared himself an enemy of the Valar.

Then Fëanor swore a terrible oath. His seven sons leapt straightway to his side and took the selfsame vow together, and red as blood shone their drawn swords in the glare of the torches. They swore an oath which none shall break, and none should take, by the name even of Ilúvatar, calling the Everlasting Dark upon them if they kept it not; and Manwë they named in witness, and Varda, and the hallowed mountain of Taniquetil, 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.

'Why, O people of the Noldor,' he cried, 'why should we longer serve the jealous Valar, who cannot keep us nor even their own realm secure from their Enemy? And though he be now their foe, are not they and he of one kin? Vengeance calls me hence, but even were it otherwise I would not dwell longer in the same land with the kin of my father's slayer and of the thief of my treasure. Yet I am not the only valiant in this valiant people. And have ye not all lost your King? And what else have ye not lost, cooped here in a narrow land between the mountains and the sea?

He doesn't declare himself an enemy of the Valar, he was simply very angry with them for not doing enough to stop Melkor.

but I suspect that the Teleri had at least some idea that to participate in his wild schemes was to defy the Valar and probably to lose something for it, and unlike Feanor, they wouldn’t do that for any kinship.

Yet they lost something by not helping the Noldor all the same.