The Dior Dilemma

[Legolas]

This gives no reason to expect that they were living immortal lives. I would expect that Dior, his children, and Earendil would've lived very long lives. Earendil and Elwing's mortal son Elros lived 500 years. I can't find any figures to give an idea of a Man's lifespan in the First Age - each date of death seems to be because the person was killed.

Still, later Elendil and Isildur lived in excess of 200 years and only died at their respective ages because they were slain. They do not appear to be withering of old age - Elendil is slain in combat with Sauron as he is leading an army of men while Isildur is murdered in the Disaster of Gladden Fields.

Aragorn lived 210 years, though that is very long for someone at that time. Even Theoden, with no immortal ancestors whatsoever, is still leading an army and fighting at age 71 when he is slain at Pelennor Fields. Éomer goes on to live to 93.

As for the twins and Nandor question, I'll look into it.