You've got some of this right but if Barbara is Nevill's confidante then she is by far the most important character of the two. Nevill confides in her that he has a premonition of his own demise. You couldn't get a more serious discussion.
Notice here the obscure way Steve expresses this. I have been led to believe that this was a suspected murder plot, the story being underpinned by Julie's admission that she supplied Jeremy with sedatives for an earlier abortive murder scheme.
Steve calls it a 'premonition'. This is over-articulation and suggests there is dissembling going on.
I cannot say for sure whether Barbara had such a conversation with Nevill on the terms she claims, but what is suspicious is that Nevill should believe that Jeremy would only kill him. Why would he do that? And reference is made to a dossier and I must wonder where this dossier is? The police and then the relatives and Barbara herself had custody of and access to Nevill's papers and effects during the relevant period.
Perhaps a guilter on here could clear all this up by starting a new thread outlining the full story for us, with the supporting evidence? Instead of telling us about 'premonitions', you can give us a precise account.
Back to Julie and the claim about sedatives. Did Julie ever clarify what sedatives were to be used and that she supplied to Jeremy? Were they prescription or over-the-counter? What brand?