Immortality and the sons of Elrond

[Galin]

Here's my theory anyway. And if it doesn't work I might try to think up another

It's based on some text from Quenta Silmarillion (section 9, The Conclusion of Quenta Silmarillion, The Lost Road And Other Writings), in which it is said:

'(...) Now all those who have the blood of mortal Men, in whatever part, great or small, are mortal, unless other doom be granted to them; but in this matter the power of doom is given to me. This is my decree: to Earendil and to Elwing and to their sons shall be given leave each to choose freely under which kindred they shall be judged.'

This is from the version of QS dated mid to late 1930s. If this idea is still in play at least (and I'm not sure that it is), Arwen and her brothers were arguably mortal by default.

This might explain why the choice was extended to Arwen, Elladan, Elrohir -- one parent had chosen the fate of Elves, the other was an Elf, and without being granted other doom their children would, due to still having some measure of mortal blood, be automatically sundered from their parents. This would be a great grief as we know, and a sundering beyond death.

If this holds water, would it not seem fair to someone who might choose an Elvish fate that his children not be automatically mortal? I mean it would arguably tip the scales of the choice before it was made, as Elrond would at least want the hope that his children could pass with him Over Sea.