For me he deserves to be tortured and die painfully. I read in a spoiler that he was supposed to be the one to go back in time and have his memories so he can fix everything. What he wanted was not the fls happiness but to save his own ass. Because apparently after the fls death their God destroyed/punish the world for killing her. So he just wanted to turn back time so he can fix the mistakes he made to save his own ass(╯°Д °)╯╧╧. Brainwashed or not he deserves a painful death.
I might have forgive him but you know why I can't forgive it is because he said that being the head of the family it is important to be neutral even in family. Wow you need neutrality to lead the family and even want to kill your own flesh and blood. What a shitty thought. When cosette came you said that I did wrong to her mother so it is time to redeem so you gave all attention to her. You forgot that you did the same thing to your other children especially the elder daughter. You deserve to be alone. I am happy that the brother is greatest treasure. He was worried about her sister till the end. I would be happy of brother and sister remain together. That shitty father can just lead the neutral life that he always wants. His wish should be granted.
People, rich families in ancient is like that, they must maintain the family's rank. Even if it's your blood related, and reason why he's not close to her? He doesn't even love her mom, he love the first wife, and FL family are the reason why his first love is dead. Even is its me, I will hate the whole family for killing my beloved.

I feel bad for the dad, first of all, they are facing cosette the DEMON not the real cosette. Ofc demons are powerful, they can brainwashed everyone. So nahhh, even if he's bad before there are flaws, like it's not like cosette is a human being.