Jane10 Yes, I think you're right re the boys ... I think there is something else to be revealed about them.
As far as the handler suggesting Alison should protect the boys, the priest gave the same advice. Finding out that they were illegitimate in those days would have been shocking, plus it would have reflected badly on Alison herself as an unmarried mother.
I think it was very common during and after the war. I know of 2 men with similar stories. One whose mother would never reveal his father's name and he didn't know why. Eventually it turned out that she didn't know it herself as he had been conceived in a one-night stand during an air raid in London when she was just a teenager.
The second chap was brought up by his mother until the war ended by which time he was 3. He was the result of an affair his mum had had while his dad was away. If his dad had been killed, she would have kept the toddler, but his dad came home and so she gave him away for adoption. He was in his 50s and had never got over it. In fact, both these men were carrying the emotional traumas.
People had secrets because of stigma.