Hi Adam when you speak of 'important discoveries' I gather you are speaking of your personal discoveries. It is common knowledge that Jeremy ate his breakfast at the farm with his family and discussed the days work with Nevill each morning, just as in any other family run working farm. It must cause a oroblem with your belief that Jeremy and Nevill had a bad relationship and also that June and Jeremy hadn't spoken for months or more, wonder if he thanked her for his egg and bacon.
Don't believe any one believes Jeremy was scared of 'little' Sheila, who was almost 5'8" not so 'little' for a woman but considerably smaller than Nevill as was Jeremy but more that he was unsure how to react to the telephone call from Nevill.
It seems Nevill was always adamant he believed in keeping family business private and no doubt particularly Sheila's illness and the problems it caused, he also wasn't a particular fan of the police, so I should think in that situation anyone would hesitate and have difficulty making a decision as to their next move. I am aware you will never agree with this, never be able to look at both sides of the argument but for all that I do believe it's a valid possibilty.
Many argue how in such a situation they would turn into action man and tear round to the farm break down the door etc. However, reality is very different, it is far more natural that our adrenaline actually slows us down in such a situation, we become more aware of danger and move more slowly.
There are always at least two sides to any story, often many more but am quite confident you will dismiss my thoughts as laughable.