Name Translations
Yamiko Hateshinai means 'endless darkness' in Japanese.
This could refer to Yamiko's power to cover everything in a shadow or blanket of darkness and trap it there.
Akumano Rasenkaidan means 'Devil's Spiralling Staircase' or 'devil's spiral staircase'. Since there is no specification that the stairway/staircase is going up or down one can assume it may be a hint on Akumano's truer nature. It also could imply his relationship towards the girls he gave fragments of his power to through a contract.
Kagayakuko Yotenno means 'shining child of the four heavens'.
Yume Hateshinai means 'endless dream'. She, as of yet, has no known power but shares her dream power with her older sister, Yamiko. Additionally she so far has not shown any relation to Akumano so this could be hinting on her role in the story.
Yukishira Itazurahime means 'naughty princess snow White' at least in proper Japanese, that is how it would be read. Fitting her power to freeze water, and create snow or put everyone to sleep.
Fukyuno Kagayaki means 'undying radiance'. It relates quite well to her fire powers.
Suspiciously she is the second character introduced to have a name related to light.