It's an odd case. The photo of her and her sisters, the little kids look unhappy. I'm no psych but she seems personality disordered. He seems to be too - and other things as well.
Definitely, child abuse, especially emotional and sexual, can develop a personality disorder in kids. So I'm sure something did happen.
But it likely combined with their overall, underlying personalities and their personal beliefs.
Her family is more vocal about the negative so we hear mostly about the mother's behavior. So it's easier to make her put to be the only villain in this case. Or at least to discuss.
If her sister is right, she was bizarrely sadistic and controlling early on
and seems to have a sick fixation on food and control. She controlled her kids through food and isolation. And seemed to get off on that. The description of her on the Dr. Phil show up was so weird. How she would make eating an elaborate ritual of control. Making her child smile before she ate. And holding her hands, making eye contact and then smiling after she was done before making her go back to isolation. It's freaky and sadistic.
There's a good article on what makes people into child torturers like this. It is very informative.
https://www.google.com/amp/s/www.bbc.com/news/amp/world-us-canada-42751715