I mean.... If you read Ashley and Koi's novel, there's a lot more details.
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Greyson and his twin sister were both born already presented as alphas which fucked up their minds from birth. They had psychopathic tendencies and no understanding of emotions at all causing them to seriously injure and nearly kill koi and chase. They saw absolutely nothing wrong with the actions they did which lead to ash needing to separate the alpha children from koi for his safety since koi is an airhead and gave in to everything the kids did. Ashley didn't want to take on the same methods his father had, but in his mind, there was no other choice since koi almost died. Keep on mind, Ash's mind is also severely damaged by pheromone poisoning from not releasing his own for most of his life.

Not the hate for ash and koi, they're my fav from all the series but yeah they're a trash/abusive parents, even tho i found it realistic and fit for them to be, especially with ash's personality