To answer recent questions, these girls are sort of bonus idols from the LLSIF game, girls who have N ("Normal" rarity) cards there.
(A popularity contest in (I think) 2017 picked the top three of these idols for what was then called "Perfect Dream Project" — and thus Emma, Shizuku, and Kanata moved from their N card-listed schools to Nijigasaki High, to be featured in LLSIFAS and the anime set to start in October.)