[Mithadan]

This is a question with no easy resolution. From the references quoted above it seems clear that Elladan, Elrohir and Arwen were granted the choice to be numbered among the Eldar or Men. The portions of The Tale of Aragorn and Arwen quoted by Galin mean to me simply that they may choose to be mortal and remain in Middle Earth until they die or they may choose to take ship into the West. I do not think Elrond's departure has much to do with it. Arwen's comment 'that choice is long over' means only that she had already made her choice and had to live and die with it.

Elladan and Elrohir's fate is a matter of intriguing speculation. They loved Men enough to fight in Gondor with Aragorn, yet they loved their parents as well. Having risked all to enter Moria to save their mother, I wonder if it would have been too difficult for them to choose to stay in Middle Earth and never see her again.

There appears to be another potential contradiction that is not addressed in this thread to this point. The Akallabeth relates that the "Valar indeed may not withdraw the gift of death, which comes to Men from Iluvatar, but in the matter of the Half-elven Iluvatar gave to them the judgement; and they judged that to the sons of Earendil should be given choice of their own destiny." Elrond chooses to be an Elf and Elros chooses to be a Man. This choice is binding upon the offspring and descendants of Elros (and leads to great trouble later). Why should Elrond's choice not be binding upon his children?