Okay, I have no idea who the others are. I just know what the source claims they are from, and an approximate guess at what they are. The second is definitely Barbariccia, the last is definitely Snow, the others I don't know.

Wow, this is a tough one. Just a bunch of minor bosses from FF gmaes.
From the artist description you can copy the names and see the original characters in screenshots with Google Images:
暗闇の雲, バルバリシア, カロフィステリ, メリュジーヌ and Snow.
I played 5 but I have no idea what their names were, even so the translated names probably weren't anything like the originals. Maybe we should just leave them unnamed.

I added tags for them
暗闇の雲 - Kurayami no Kumo (Cloud of Darkness) (FFIII)
カロフィステリ - Calofisteri (FFV)
メリュジーヌ - Melusine (FFV)

Snow is a colorswap of those chicks in the Temple of the Ancients that appears on the Northern Continent, right?

Yeah, Snow was one of those underdressed female monsters on the Northern Continent.