Actually the og fl survived due to something they did but due to not being able to sacrifice someone something happened to the father which made him kill his family the only person to survive was the og fl. (This is according to what I remember, it's been a long time when I last read it)
Soo there was a theory (from the previous version because it seems this is a remake) the leader of the church who demand sacrifice, is the fake sister's (og fl) real father (they have similar physical features) . He wanted his daughter to be the heir of that family. So he created a false prophecy (?) because hes confident his daughter has charmed the duke therefore he could kill the fl covering it as a holy sacrifice , but the duke choose the fake daughter instead so he became angry, save his daughter and curse the entire family thats how they went down. Its just a well known theory from the previous version of this manhwa/manga
MAJOR SPOILER BTW
I’m confused….so she wasn’t chosen to be the sacrifice but she still dies? Isn’t it a good thing that her father didn’t choose her to be the sacrifice? I feel like I’m missing part of the story or maybe it’s an mis-translation sort of thing?