Born in T.A. 130, Elladan and Elrohir have one younger sister, Arwen. Though Tolkien never specifically states that Elrohir and Elladan were twins, many clues were given to prove this possibility. First, they are described as "So much alike were they, the sons of Elrond, that few could tell them apart: dark-haired, grey-eyed, and their faces elven-fair, clad alike in bright mail beneath cloaks of silver-grey". Second, one is rarely mentioned without the other, and their names are only separated when they are speaking. Third, they were born in the same year, while most Elves wait at least ten years between children. We are not told which twin is older but every time they are mentioned as a pair, Elladan is always first and many historians have accepted that Elrohir is the younger of the twins.
The brothers were friends and companions-in-arms of the Rangers of the North, and helped defend the remnants of Arnor from evil after the fracturing and fall of the Northern Kingdom. Five centuries before the War of the Ring, Celebrían was captured by Orcs and tortured. Elladan and Elrohir rescued her, slaughtering the Orcs, and their father healed her wounds, but she soon departed Middle-earth. Ever since, they held a special grudge against the Orcs because of their mother's suffering at their hands. During the War of the Ring, they fought alongside Aragorn in the battle of the Pelennor Fields in Gondor.
Like their sister, father, and uncle, they could make a choice between mortality and immortality, expressed by whether they would follow their father to Valinor at the time of his own departure at the end of the Third Age. Since they are explicitly described as remaining in Rivendell for a time after their father's departure, it is believed that they may also have chosen to depart from Middle-earth. However, Tolkien never wrote what their choices were, but noted that they were allowed to "delay" their choices.
