The proper third-person form for a queen would be "Her Majesty."
Does this apply to members of her immediate family too? As for when a princess is saying that she is somewhere because her mother the queen did something?
Unsurprisingly, googling "third person" "queen" "address" and just about any other term I could think of turns up the general rule.
Peter, the overly-inquisitive nephew of my main character, is 23 years old and the only son of a minor Squire in the Lake District. He lives with his uncle in London (and is learning far too much about certain cultures there - he really shouldn't have been taken to the Lilypond), or he visits home.
1) I'm assuming he would have studied and received a degree. I'm tempted to send him to Cambridge, and would prefer to avoid Oxford (because it's used all the time), so apart from London, where else could he have gone?
2) While he's having a lovely time being a young man about town with a little money, one day when his father dies or is just too old to look after the property Peter will be expected to take over. (Of course in 1932 they don't really know that WWII is coming). What sort of occupation could a young single man with a degree take on that would be respectable, but that he wouldn't be expected to make a career out of? I don't think the church would suit him, and he's not the Army type (although his uncle used to be a Major).