Going back to the original post, the timeline of the calls is a little odd. If JB got a call from Nevill at 3:10 and didn't call the police until 3:36, what was he doing in the intervening 26 mins? That's a long time to wait if you are worried your sister is threatening your parents with a gun 
Bob, Jeremy had witnessed all this before.
Shiela [poor soul] had exploded many times, ie gas man, When June calmed her down.
Maybe the rejection by Colin was the final straw.
If that's the case then why call the police at all?
Bob, in my mind it had escalalated from previous occurances. With this in mind I can see why Nevill sought Jeremy,s help. This was something he had not seen before.
By the way Bob can you start the thread that you spoke about, as I think it was interesting, and will help in determining the chaff from the wheat,or visa versa.