The older sister is literally asking to lose, she knows he likes her and already saw that her sisters are developing feelings for him but instead of being clear about her feelings, she wavers, stays unclear and even makes some space for her sisters to get in…
I’d usually root for the big boobed onee-san, but here if the middle sister wins I wouldn’t complain. Obviously i won’t root for the youngest for 2 big reasons her sisters have and she don’t
Thanks for the translation