Eluréd was Oropher, King of the Woodland Realm and Legolas' grandfather, and Elurín was Amdír, King of Lorien before Galadriel and Celeborn ruled.
I have a headcanon that Maedhros and Caranthir were really close in Valinor. Turko and Kurvo were already in separable, and the twins go without saying, while Káno was everybody's favourite musician with no end of admirers and performances.
Nelyo loves all his brothers, of course, but he sees his younger, easy to anger, always blushing, awkward, and a bit overshadowed brother and gets fiercely protective. He is there with Moryo to support him and help him work through his emotions. His brother is reactive - always - so he helps him talk through why he got so angry about Angaráto's taunt or Findekáno's joke. Moryo is shy and uncertain so Nelyo always makes sure that he actually does what he wants to do without being shouted down for being boring by Turko and Kurvo especially.
When they swear the Oath, something changes. Moryo regrets it immediately but sees that his brother, the ever resolute Nelyo is just following their father like the rest of them. It cracks his faith in his older brother which is only worsened when he sees Nelyo at the burning of the ships finally seeing the foolishness but doing nothing to stop their father when he's the only one that could get through to him.
Their father dies and Nelyo becomes king but then he abandons them to go on a suicide mission to try and outsmart Morgoth. By the time he returns, broken and carried by a Ñolofinwion, Moryo is just angry with him. For sailing in the first place, for never stopping their father, for falling for Morgoth's trap, for putting them in debt to Ñolofinwë and his people, and, the last great injustice, handing over the ruling of the Noldor to Ñolofinwë.
He gets angry and he lashes out at Angaráto which, in turn, makes Nelyo angry at him. They fight and Moryo accuses the still-recovering Nelyo of many things. It breaks the trust between them entirely as Nelyo agrees with all of his hateful words and Moryo would do anything to take them back but his pride won't let him.
They separate - becoming Maedhros and Caranthir - and they become distant from each other. Maedhros becomes incredibly close with Maglor as they support one another while Caranthir convinces himself that he likes to be alone.
By the time Caranthir dies in Doriath, they have barely spoken outside of battle plans and finances in centuries.