It is intentionally blown out of proportion. He explained what the boys didn't like. They didn't like the food they were served while staying and didn't like being taught about religion, having to do chores... They were probably allowed to do anything they want except when at WHF where they had to do as they were told and were made to do things they didn't like.
People who harp on such do so in order to push an agenda it is not an accident. It is used to try to suggest June and Nevill were horrible people though it is quite ridiculous to suggest this establishes such.
I'm sure they didn't, and encouraging them to do things they don't like WASN'T necessarily bad for them and may have helped them develop. HOWEVER, there are ways of doing this. Forcing them isn't one of them. Make things seem like fun. Engage with them. Sadly, June's way of handling her grandsons seems to have been, as it had been with Sheila, about control. She seems determined that they would do it her way. I see nothing wrong with bringing children up with Christian values but although I don't believe it was her place to do this without the parents' permission, she could have taught them religion without the word ever being mentioned. Surely much better to turn bible stories into adventure stories that she could have told them off by heart instead of reading them in language which isn't easy for children to comprehend. Might it not have been better simply to teach them how to be kind rather than have them on their knees, praying. Her way put them off, even frightened them.
Even when I thought that Jeremy was innocent I didn't suggest that Neville and June were "horrible people" -certainly Neville was thought of as being great fun and excellent company. June was a worthy woman who I believe was kindness itself to those she didn't have any expectations of. Sadly, she had expectations of her family that they appeared unable to fulfil.