Neith/"Nate", The Chariot candidate, isn't really going to be Yuuto's enemy due to her overall personality and such being timid and shy, but she does help him in one way during this 2nd arc. (She'll take a liking to Yuuto soon too)
Stella, the Star candidate, is just doing what Stella pleases for the moment as she's currently an idol in the human world and keeping her Star candidate side 'hidden' from said human side ish iirc (She more or less has some kind of interest regarding Yuuto, mainly regarding Lizel obviously, but that's as far as I know currently from where I left off in the LN)
The other candidates varies for as far in what they do and such since we only got to know some of them in the LN compared to the few others that have yet to be seen, appearance wise (apparently, this LN series is part 1 from what I heard from some reviews on MAL on the LN series of up to Volume 5; dunno when we'd get the sequel LN part 2 and such regarding the other demon king candidates)
Like how Mahouka is completed and has a sequel series, Magian Society or how it is titled as