Very trivial stuff from dat one page:
The one translated as "Imperial Knights" are 近衛騎士団(konoe kishidan), according to the dictionary "konoe" means Imperial Guards; Personal Guards; or Royal Guards.
The one translated as "Royal Knights" are 王国騎士団(oukoku kishidan), "oukoku" means kingdom; monarchy.
"Kishidan" means, well, you know Code Geass and the Black Knight Order.
Rather clear in Japanese, turned out weird translated?