The Royal Siblings remind me of Helios (Sun) and Eos (Moon), because both characters have the duty of rising the Sun (Celestia) and the Moon (Luna). I'm certain that they were based on greek mythology.
Little Sister :'( this was when Luna was the mare in the moon. i bet she took on twilight sparkle as her student becuse she reminded her of her lil sis and her names twilight-(see what hashbro did there?)i bet thats what she fellt all those years
Luna and Nightmare Moon is strangely similar to The Meta and Sigma from Red vs. Only Nightmare Moon is a alternate personality Luna created to cope with her own loneliness (or completely different being in the comics.) while Sigma is an A.