The Númenóreans (at least the kings) are the heirs of Elros who was the son of Earendil and Elwing and so had ancestors in all houses of the Edain and all groups of the Eldar as well as among the Ainur.
The Kings mostly (or often) wedded their relatives to keep the line "clean", but after some time when the shadow fell over Númenóre they lived shorter and shorter, yet they still had halfelven blood and so lived longer than the so-called "lesser men".
The daughter of the fourth king, Silmarien, wedded the lord of Andúnie and her son became the next Lord of Andúnie; The people in Andúnie (in contrary to the kings) always stayed faithful to the elves and kept the contacts; one of the last Lords there was the father of Elendil the Long whose sons Anárion and Isildur founded Gondor and Arnor together with him after the downfall of Númenóre.
Also the Lords of Dol Amroth are related to the Númenórean kings - the first Lord was the son of a Númenórean related to Elendil.
The kings of Númenor were
Elros
Vardamir
Tar-Amandil
Tar-Elendil
Tar-Meneldur
Tar-Aldarion
Tar-Ancalimë
Tar-Anarion
Tar-Surion
Tar-Telperion
Tar-Minastir
Tar-Ciryatan
Tar-Atanamir
Tar-Ancalimon
Tar-Telemmaite
Tar-Vanimelde
Tar-Alcarin
Tar-Calmacil
Tar-Ardamin
Ar-Adúnakhôr
Ar-Zimrathôn
Ar-Sakalthôr
Ar-Gimilzôr
Tar-Palantir
(Tar-Míriel)
Ar-Pharazôn
(the names that start with "Tar-" are names from kings faithful to the elves, the others (ar-) were mostly not)
uh. yeah. what he said. and............. Elrond is called Elrond the half elven because of his mother marrying a mortal. their two sons, elrond and the other ones were given the choice to be elven or mortal. elrond's brother chose to be mortal, so his line, which includes aragorn, live much longer than other men because the valar allowed them a longer lifespan. feel free to correct me if i'm wrong!!!!!
Originally posted by Maikahyandowen
Elrond is called Elrond the half elven because of his mother marrying a mortal.
Elronds mother was of elven blood but even had Ainur blood (as the daughter of Dior who was the son of Lúthien and Beren; Beren was also human but Lúthien was half-Maia, half-elven), while his and Elros' father was Earendil who is kinda difficult to explain.
Earendil was the son of Idril and Tuor, Idril being the daughter of the Noldor king Turgon of Gondolin, while Tuor was mortal, too - son of all three houses of the Edain. But Earendil got one Silmaril and sailed over the sky with it, so he is immortal but yet of mortal kind 😄
So Elrond and Elros are some thirtytwoths mortal, some elven, and one sixteenth Ainurean blood 😄 😄
They also say that Arwen is an exact replica of Luthien and Arwen's whole romance thing with Aragorn brings them back to the tale of Luthien and Beren. Elrond and Elros are the sons of Earendil and Elwing.
I'm just adding some info from Exa's lovely answer, that After the Downfall of the Numenoreans their life-spand became ever shorter, originally Numenoreans has a lifespan of 100-300 years. Aragorn died when he was around 120 years old. And this is because he's a direct descendant of the Numenoreans, on Isildur's side in which he ruled Gonder. Isildur's brothers ruled Arnor.