well, according to the NovelSo what happens to the younger sister? None of the brothers like her now
the big bro still kinda holding to her since he still thought MC still like her.but the moment she find out that it was MC who saved her big sister and not the big bro, she flipped like a frickin Commute train doing Kansai Dorifto and want the MC instead. but well, at this point MC and big sis already in mutual love and technically in relationship (also basically this whole show and progress of their relationship was Carried by the big sis)