I find all the different points of view confusing.
We simply don't know how terrified Nevill allegedly sounded. He didn't actually say much did he? It seems that Jeremy rang Julie, and she told him to go back to bed. Perhaps he thought at first it wasn't that serious, then thought it might be, but not enough to ring 999. Perhaps he wasn't that bothered what Sheila was doing. Perhaps it didn't occur to him that the whole family would be shot.
It's all speculation anyway.
Or is it that you're confused about what you think?
We actually DO know how terrified was Nevill.
A) He allegedly got his son out of bed circa 3am to tell him
B) We have Jeremy's word that he'd sounded panicked/terrified.
I'll grant that it's extremely difficult to decipher how Jeremy was feeling about something I don't believe happened, however, he pulled it out the bag eventually and went through the motions.
Some of the padding may be speculation. The facts aren't.