You know Jane I sometimes get the feeling that Jeremy is repeating things he heard from June, and maybe in fairness at seventeen years old in a light-hearted way. One recalls his remark to Roger Wilkes that it wasn't until 1978 that problems arose, though of course there is no further elucidation in any of the books on the case. After her second illness June began moralizing again, affecting both Sheila and Jeremy, and maybe anyone in his position would reject what she was saying. The tragedy is that there were no roots as a family, no bond on which to fall back on of cheery, carefree times: just a void, wherefrom emanated the germination of an idea that all were incapacitated in some way and that meaningful life had ended for them,his justification for killing the twins being that they too would in time become affected by this void as had Jeremy in his turn. The practical side of him however, the Jeremy who had facts and figures to hand at the Osea Road board meetings was not going to run the risk of June leaving a substantial legacy to the Church, or of disinheriting him altogether, as he told Julie was his main concern.
Steve, many children emulate parents. We recognize it because adult "speak" sounds inappropriate when spoken by children. They take on an out of place superiority and arrogance when spoken by adolescents. It is said that imitation is the sincerest for of flattery. This is really all that children are doing and in so doing, there looking for approval. The more approval is withheld, the more the child will emulate/flatter.
Children often take on the responsibility for a parent's well being. Let's suppose that shortly after a child has broken a precious ornament, it's mother is rushed into hospital, the breakage is no longer thought about, but the association, to the child, unless it's spelled out to the contrary, is that Mummy was ill because he/she had done something naughty. God forbid, should Mummy die, the guilt will stay with the child forever because A) No one has told them otherwise. WHAT broken ornament? and B) Because the "child" at whatever age will feel too ashamed to admit it was responsible for it's mother's death.
I'm categorically NOT saying that this was definitely the case with Jeremy and Sheila, but I well remember being told that children shouldn't be praised because it made them conceited. Such children are very likely to go to extra lengths to gain approval.