Harold & ILBW - concerned that they will become irrelevant if they don't attend the Coronation - que?
So if they don't attend (if they are invited) then they will become irrelevant!!!
I read this as they really want to go, they want a major part so they remain relevant .... if they don't go because they won't have prime billing, then they will be irrelevant...
look Harold - it is really simple - you get an invite - you go, because it's your father's Coronation - you accept whatever role you are given/not given, with thanks and no fuss. You go back to the US. People will appreciate that you went, you were relevant in your proper place.