Please note there aren't official A casts and B casts this is just the combination I saw first! Featuring:
Aragon - Lee Arum-soul (이아름솔)
Boleyn - Pae Su-jeong (배수정)
Seymour - Park Ga-ram (박가람)
Cleves - Choi Hyun-sun (최현선)
Howard - Heo Sol-ji (솔지)
Parr - Yoo Ju-hye (유주혜)
(also please forgive the fact that the image features son seung-yeon, kim ryeo-won, and hong ji-hee instead of lee arum-soul, heo sol-ji, and yoo ju-hye as i could not find a pic of the six queens combo i got!)