Responses
I think it's because they believed their father when he said the mother died after giving birth to the last ones and didn't question his authority.
Ray, Raphiel Jr., learned the truth because of him seducing Linus, who knew about all of Kloff and Aeroc's actions. But he was suspicious of the fate of his mother since he was a child but it wasn't until he was an adult that he confronted and exposed his father's terrible actions. Same with the other children I guess.

... is it that older kids never asked questions like where's their mom etc whenever they get a new siblings???
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