They could not use the word "Royal" as part of their brand name in the UK.

That's not the same thing as never being able to speak or write the word "Royal" in an advertisement. Anybody can claim that their product will provide a "royal experience" or make you feel like a "royal" (or a king, queen, prince, or princess, etc.)

I loathe the twosome, but people need to keep a sense of proportion about what they can and can't do. Or what Charles can or can't do regarding their behavior.