After reading some of the chapters' comments, I see people want Tsukushi's injury to have been an accident after all.
On the one hand, I of course want all the Onee-sans to be innocent, so we have no reason to dislike any of them.
On the other hand, the possibility of an accident was examined by the investigator, and dismissed on some pretty convincing grounds.
So, while I'd like for the author to exonerate all 3 sisters, I'd prefer a development more convincing than “Whoops turns out he fell after all teehee!”.