Frothy said:Of course do not curtsey to pretenders like the Greeks - or anybody else who affects a royal title when their nation is a republic, eg, Serbia, Austria, France etc. The exception would be Princess Anne-Marie as she is still a Danish princess, but I would not be saying the words "Your Majesty".
Constantine is Prince of Denmark (who married a Princess of Denmark) and all the kids inherited that title after their father, not their mother. Pavlos kids are to, but not his wife.