Both “your majesty” and “his imperial highness” are used as titles; thus, all those words should be initially capitalized: “Your Majesty, His Imperial Highness summons the prince to the Command Council's tent.” ... (Also, if there is an official body called the Command Council, by all means capitalize its name.

Should the King be capitalized?

'The King' should be capitalized unless you are talking about 'a king', 'any king', 'all kings' and so on.

Should the Queen be capitalized?

It's 'Queen Elizabeth,' she's the 'queen': "Capitalize king, queen, prince and princess when they are used directly before one or more names; lowercase when they stand alone," AP Stylebook says.