Only one lineage?

[The Saucepan Man]

What is significant about Elros, Elrond and his children is that they did have a choice. The default rule, if not known at the time, was that any amount of mortal blood made one mortal.

My understanding is that, once Elrond and Elros had been given the choice between mortality and immortality, all children of a union between Man and Elf were to be given the same choice. Is that right? And, if it is, should the children of Imrazor and Mithrellas not have been given the same choice?