I agree that upbringing and environment does have a bearing on a childs' future. Stability being the most important of all.
Where there are two parents,,and one is " unstable " then it's the turn of the other parent to retain a balance.
This would have been difficult for the Bambers on account of Nevilles' demanding work,so the onus was on June in her task of bringing up two children when she was already mentally fragile.
I can't even think how the adoptions came about. Whether it was because her family had children,,whether she was lonely when Neville was farming,,,whether she thought it was a right for women to have children,,,whether it was that she wouldn't allow her own infertility to get in the way. We don't,,and will never know.
Nevilles' view would have been different in that if a boy came along,then he would see him as a farmer like himself and so would prepare him for the future.
Neville possibly also suggested the private schools to give the children a better start in life,,and the boarding would give June the break that she obviously needed.
Girls invariably behave like their mothers in lots of ways,,and Sheila would have picked up on Junes' problems from an early age,and would have developed a nervous disposition which would have shown itself in future years. I'm sure that Sheila wondered at times what was happening to herself,poor girl.
Sheila was unsettled at school,,possibly because of an inner confusion of being away from the security of home,and freedom on the farm. I don't think Sheila was a girl that could,or would tolerate being out of her comfort zone,,and would imagine that her behaviour was somewhat trying at times. Sheila did what Sheila wanted to do,,,your normal,wilful child ( who are difficult to rear ) and unless a mothers instinct kicks in,,then you see the child as one who is badly-behaved.
June didn't have that motherly instinct,,which is obviously so important if you want to get to know your child,and their reasons for being wilful and frustrated,as half the time it's a mark of sadness which a child can't always explain like an adult can.
There are some mothers who are " made " for the job,,and there are others who aren't.
