I don't know if you were joking when you said Actual Egypt only had one sphinx, but if you weren't: it's not correct. The sphinx was a very common iconographical image in Egyptian sculpture, representing a manifestion of the sun god, or a king's manifestation as the sun god. There are a great many sphinx statues - though, to be fair, Khefren's sphinx at Giza is the only attested one of that monumental size. :)
And yes, I was joking.
By the way, I’d love to hear more how you feel about the set.