The nature vs nurture argument is a lot to unpack. Parental orientation has been interpreted in a many ways – but the enneagram field has largely rejected the idea that enneagram type develops due to “nurture.” The common interpretation is that parental orientation occurs because of your nature.
Arguably, two siblings might respond very different to the same parents because they are naturally two different types; so the child ‘invites’ the particular parental orientation associated with their type. Still, even that has been under scrutiny, because in a lot of cases, it just doesn’t add up with reality.
In order to make sense of it one must dig beyond the surface. For instance I’m a four. Fours are supposed to be separate from both parents, but I was close with my parents. So what does this mean? It means I focused on an identity that was inherently alien or separate from them, developing my own personal mythology on an alien world, and spending most of my brain-power on that “dissection of self’ rather than on family matters. It doesn’t mean I wasn’t close to them.
I’ve seen countless stories where people claim that they don’t match their type’s parental orientation, but upon talking to them further it’s more that their nature invites this orientation with others. For instance, they look for mothers and fathers, nurturers and protectors, in other people in a certain manner that displays their type. Two siblings do this differently, according to their own type’s makeup.