I disagree. I recommend that you, and everyone read “My Brother’s Madness” by Paul Pines - an eloquent and heartbreaking book about his surviving a deeply disturbed family. His brother, who was younger, was driven mad. Biology had nothing to do with it.
Mentally ill parents can have normal children just like normal parents can have mentally ill children.
Escaping a disturbed family doesn’t prove that mental illness is not biologically based.