British peers of the higher ranks tend to have lower, subsidiary titles that they were promoted from or otherwise obtained. So a Marquess of X might also be Earl of Y, and Baron of Z.
According to my understanding, his eldest son gets to call himself Earl of Y (or Lord Y), and his eldest son gets to call himself Baron of Z (or Lord Z). But what happens if the Earl of Y dies in a tragic gardening mishap? Then the succession to the Marquessate moves over to the Marquess’s second son. Does the first grandson now have to give up using the title Lord Z? Or does he get to continue using it in a way similar to how former U.S. Presidents are still called Mr. President?
I’m curious about this situation because until I thought about it, I didn’t think it was possible to lose a title once you were entitled to start using it. And I don’t recall ever reading about such a situation in any novel, or anywhere else.