Who are these characters referenced in chapter 4 of Spotted Flower?
They're from a Visual Novel called Kizuato. The names are (in order of their pictures):


Kashiwagi Hatsune (柏木 初音)


Kashiwagi Kaede (柏木 楓)


Kashiwagi Azusa (柏木 梓)


Kashiwagi Chizuru (柏木 千鶴)

As for "Kashiwagi Azusa"'s name (柏木 梓), I'm not sure why it was translated as "Azuki", but if you look at the original Japanese:



It says "Azusa".