To get a king or queen’s attention, you should say, “Your royal highness.” Do not say “Hey you there!” or “Queenie.” You may use their first name if you happen to know it (e.g. “Elizabeth”). No nicknames, please.
If you meet a prince or princess, address them as “Your slightly less royal highness,” or by their first name.
Grandchildren do not rate until they’re married, and then only if they marry respectably. You can use nicknames and treat them as you would any other children, except that you have an additional tool to keep them in line. If they misbehave, tell them, “Remember, Billy,” (or whatever), “the nation is looking to you as an example. Don’t disappoint your subjects.” If you do this, the little future prince might quit hitting his sister. Or, maybe not.
Royalty do not have last names. Do not ask them what their last names are, because they will be embarrassed at being unable to tell you.
All types of royalty like to be complimented on their shoes. Remember, no nicknames, so say, “Nice shoes, Charles!” not “Nice shoes, Chuck!”
Some also like to be complimented on their hair, but others may get offended if they think you’re trying to flatter them. The safe thing is to ask where they got their haircut; if they’d like a compliment, they’ll ask, “Do you like it?”
If the royals’ crowns are crooked or their buttons are buttoned in the wrong holes, do not draw this to their attention. They have minions for that. Let the minions do their jobs.