It's been quite a long time since I've finished the novel, but, basically, her sister put a curse on them: the more you love someone, the more you will feel the opposite of your true feelings. I think it was like that, please correct me if I'm mixing novels ^^
On first timeline the family was already brainwashed before MC annd Lorena came to the mansion. The main villain had done it. He used judical law and magic. It's not a curse. After Lorena came, the brainwashing was getting stronger. That's what I remember. And that wasn't because of Lorena's curse, the black magic in nacht's house was the cause: the more they love the person, the more they would hate/be indifferent to them. It's not that they didn't love her but the magic made them hate/forget her plus the brainwashing. But in second timeline it didn't work because Sienna unconciously purified the house and the main antagonist couldn't get near them.
