Tidbit: When Tony and Margaret were married Prince Philip was the only adult "Royal Highness" in the family to give Tony permission to address him by his first name. For the rest, Tony had to "Sir" and "Ma'am" them. He was told by Margaret that he was allowed to call Charles and Anne by their first names, but only in private. Charles and Anne called him "Tony" and never "Uncle".
That's pretty dreadful back in the 19th century stuff, and in the early 1960's would have been considered quite normal. Just reminds us how far we've all come since the formality of those days. Of course, it was a much smaller royal family then, so there wouldn't have been many adult males for Tony to call Sir anyway.