Added a bunch that were missing (Aki sisters, Nitori, Suika, Iku, Tenshi), but I can't tell who's in the very back behind Iku or China. I think I see Hina behind Komachi as well? Bow is the only hint.
I'm thinking Wriggle and Mystia behind (the insert of) Meiling, and that looks like Youmu's vest between Eirin and Keine. Not enough to go on for the girl behind Iku, though.