Comment by SIMPai chottominute on Terminalnavy

Iirc, it was bcs they feel somehow fond and sort of remorse towards Sienna which they don't understand bcs they don't know her in this life. Those feelings stemmed from their feelings from their past lives. They genuinely liked Sienna but that btch did smthng like black magic (forgot the terms they used here) on the whole mansion which affected everyone tied to it like the nacht family and the effect was especially strong on Aciel who is directly tied with the house (it'll be explained in the future),and the magic is about the more you like Sienna, the more intense your hatred or negative feelings toward her will be, that's why Aciel was the one who mistreated her the most in her previous life because he loved her the most. We will also get a sneak of their past lives specifically, after Sienna died. Aciel went crazy and turned back time.