Queen - yes, as far as I know the idea is to switch the main cast every two years. Maybe for Edward and Andrew - who've only been seen as babies so far - they will only get one series out of the actors, like they have with Charles and Anne. They might get two series out of the new Anne, who hasn't really changed as she's aged, and I wonder if Helena BC will be the last Princess Margaret?
Maxima's green thing looks very complicated. I can't really work out what it is meant to look like!!