too much time has passed for only one person to blame.
it's been almost 20 years since Perrian got snatched away. the whole fam not moving past Perrie's disappearance, aside from Pandernian and Perrian herself, just puts all of them at fault, not only because
"boohoo we couldn't protect her"
but also...not moving on or genuinely figuring things out beyond seeing if she was DEAD dead
anyways
dad is an insecure deadbeat
eldest bro is an obsessive [potential] necrophiliac
second bro is a sis-deprived siscon
ironically, after writing all this down, this means i personally find the creepy grand duke less effed up compared to Perrie's family.
TL;DR
yeah the creepy male adults are sick in the head, but let's also not forget how everyone except the adopted kid CHOSE not to move on properly from perrie's disappearance.
I just think from the latest chapter, when she got taken away, they thought she was at good hands. And when the older brother decided to visit, he saw many of her bodies there, which he probably thought she was dead. There are people who's not at fault but still feels guilty, as sending her away was probably decided by the head of the family. But this is just my opinion alr

Just as guilt was planted in the brothers' mind, perrie also had some hatred in her. Sad because true to that one comment, the father is responsible, I can't even blame the brothers since everyone kept saying the mc is an illegitimate child, and the father didn't trust he wife enough just as the wife was too carefree to explain. The kids suffered from what they heard, they loved the mc but as children they didn't have power to help, and they didn't know what was happening to the mc too. "They could've visited her to see" they were grieving for the duchess, I could excuse the kids since they're children, but the father? Nah
I don't know, this is just my opinion on what I saw about how they grew up