Prince Imrahil's elven descent

[Man-of-the-Wold]

Well, I don't know how this is reconciled. Amroth and others of the Silvan Elves were probably Eldar, in that they were descended from the Teleri of the Second Sundering, the Nandor, which also populated areas of what became Gondor and Eriador at times up thru the Second Age. A part of this group also eventually entered Beleriand and were the Green-Elves, who also accompanied Grey-Elves in the Second Age in colonizing the Eastern Woodlands.

The Green Elves were sort of intermediary between the Beleriandic Sindar who knew the influence of Thingol & Melian, and the Non-Beleriandic Nandor, who were still in some sense Eldar.

The Avari were left in the rather distant East, and they apparently never had any longing to ever go to Valinor, whereas with the Sindar, Laiquendi and Nandor the longing merely slept.

Some of the Wood-Elves of Thranduil's realm may have been in large part derived from Avari, however.

Seemingly, though, Amroth, Nimrodel and any of the Elves venturing to Gondor/Edholland in the Second through Fourth Ages to pass over the Sea (if not Sindar/Noldor) were Nandorin. True Avarian Elves would not have had this desire for the most part.

Imrahil's Elven ancestors were not necessarily related to Amroth, but was/were apparently an Elf-maiden or two who eventually went West, after bearing the child/children of a Gondorin Dunedain, as described in the UTs.

What I think the significantly difference here is that Luthien and Idril were not only much greater, but the nature of such offspring in terms of being Elf or Mortal was undetermined until the end of the First Age. And, it is only through these unions and the crowning one (pun intended) of Aragorn and Arwen, that the blood of the Firstborn was introduced and mingled with that of Men.

After that the Valar probably made it such that any other offspring of Elf-Man that might later arise would simply be Men and Women, and notwithstanding how Imrahil's ancestors who were born of such unions seem to have carried superficial Elfin traits in terms of appearance and what not, they were not Peredhil, like Earendil, Dior, Elwing, Elwing's brothers, Elrond, Elros or Elrond's Children, nor were they like Arwen's children, who were nevertheless Mortal.