The Unions of Elves and Men

[Huinesoron]

NoME comes to the rescue on Dior: 1.IV "Time Scales" says: "Twins were very rare, and [Amrod and Amras are] the only case recorded of the Eldar in the ancient histories, except for the twin sons, Eldún and Elrún, of Dior Eluchil, but he was half-elven. In later times (Third Age) Elrond had twin sons." That's a ca. 1959 text. He's also directly called "Dior Halfelven" at the beginning of HoME XI's "Wandering of Hurin" (entry for 497), though that doesn't necessarily mean anything for his lifespan. (Since I brought up the boys living longer: Home XII explicitly says they died, in "Problem of Ros".)

NoME is also explicit on Arwen, but throws in a brand new surprise!

Originally Posted by "Nature of Middle-earth 1.XI Aging of Elves"

[Earendil] obtained the grace (from Eru via Manwë) that his children, being half-elven on both sides - descendents of Idril and of Luthien - should (a) have a choice of which kindred they would belong to, and (b) should in each kind have "a long and fair youth" - sc., should only slowly reach maturity - and that this should extend to the second generation: thus Elrond : Arwen and Elros : Vardamir.

... Eldarion was mortal and was not by promise included in the "grace of Earendil"...

... [Elros] lived at the Numenorean rate and died at the age of 500 (voluntarily and therefore not at very great age)... Vardamir lived to be 391 and so was little more than normal Numenorean age (300).

A draft of this passage actually extended the grace to the third generation, giving Eldarion and Tar-Amandil the same choice, but this was rejected. Vardamir wasn't! It makes his rejection of the sceptre even more significant if he was also rejecting immortality.

It's worth noting that Elros had three other children, so the possibility of immortal half-elven from his side is there. Nothing is recorded of them or their descendents apart from the trio's names.

Back in "Elvish Ages & Numenorean", we can read that "At marriage Arwen became 'mortal'", and about "had she remained Elvish". Elrond is described as having been "made Elven" after the fall of Thangorodrim, while Elros is said to have lived out his life half-elven, and to be the only one who did. So it seems like Elrond and Elros had a weird lifespan due to their parents both being half-elven, but were natively mortal; they were given the choice to change that. Their choice would pass to their children, but those children could choose to reverse it for themselves and their descendents.

None of which has much bearing on the question of elf-mortal marriages, but I'm pleased that the answers actually exist.

hS