With Mutsuki it's debatable what her feelings are because it can easily be brushed off as in the grey area, but jesus Yayoi is romantically into her brother huh.
@Duckerby I fell you.Rooting for siblings to hook up is weird but so are Haruki's friends that describe his sisters as his harem. And while the chances are getting slimmer and slimmer after each flashback there might still be a small chance for you and me. I'll just quote myself:
There was a hint about that in chapter 3
In chapter 3 Haruki refers to his parents and the kanji is apparently read as "foster parents" according to the translator. If that was the case Haruki's appearance with his sisters in the flashbacks does have to be explained. Maybe he has been adopted very early or he was a childhood friend of sorts. They sometimes call their friends by nii-chan and so on