Eowyn, Eomer.....Their Lifespans?

[Nilpaurion Felagund]

Whether one parent is elven the other is mortal, by blood you could be half-elves, but Manwe puts the "choice" on people, like Earendil and Elwing's sons, Elrond and Elros. (Boromir88)

To elaborate on this: Manwë (under consultation from Eru) gave them a choice, because Elf-Man offsprings are mortal - yes, Dior is mortal - and are banned from stepping into the Undying Lands. Mandos raised the question himself, and Manwë gave the choice as an answer to his question - frankly, I have no idea what would happen had Eärendil or Elwing chosen to be of the Atani. But they didn't.

The choice was extended to their children, and their children alone, because of some reward. Since I don't have the books with me, I forgot the right reason. But there.

Oh, and hope this helps. It's about the Rohirrim and the Númenórean blood.