Then surely they would have shared certain traits? Abandonment, insecurity, disloyalty? Why did JB steal from the caravan park, knowing how much it would upset Ralph?
Jeremy was a rebel who was able to resist June's control, partly, I believe, because he was male and, as Colin said, had a strong sense of identification with his father. Though this wasn't without its problems. Nevill was a control freak too in his own way - for goodness sake, he would have turned Jeremy into the English equivalent of one of the 40 year old farm boys of County Clare if he'd had his way! You've said as much yourself, Shon'. Yet Nevill wasn't loopy. Identification with Nevill gave Jeremy a grounding in reality which Sheila could not and did not get from June.
Sheila's role model was her religious obsessive mother who had deep psychological issues of her own.
I think the theft from the caravan park was an understandable, subconscious attempt by Jeremy to assert his own independent identity. My son and daughter behaved in very similar ways. The limpet like suckers of smothering parents are only detached from their almost adult children by a very painful process, one which forces parents to dislike and reject their children for a time.