[Mithalwen]

For the sons of Elrond, the comment "stayed a while" could equally imply that they then left. There may have been a grace period, some sort of mopping up operation perhaps. Arwen of course had made her choice prior to Elrond's departure and having thrown her lot in with Aragorn she had made her choice for ever - else Elrond might have remained the trivial in Elven terms span until Aragorn died.

As for the children of Elros not being given the choice, well while they of course had majority mortal blood and married mortals, I think it was more of a case of the Gift of Iluvatar being too precious to be denied anyone who was remotely entitled to it.