If Neville phones Jeremy. There is a chance he may not answer. Fact.
There are 18 more.
WhenEVER a call is made, irrelevant of to WHOM, there is always a chance the call won't be answered. However, when one is in ANY stressful situation, rationale doesn't come into the equation and one calls the first person who springs to mind. It's ENTIRELY unsurprising that in this case it was Nevill's son. That father and son will have had their differences wouldn't have negated a relationship going back 25 years.
I can see a situation where the caller is having doubts. Do they put the receiver back on the cradle? Do they let the phone ring a few more times? Do they drop the receiver/put it down to check on what may be happening? What Nevill May or NOT have done under "normal" circumstances is likely to have been quite other than what he may have done in an "act first, think later" situation.