Please advise as to when to use jr pass

Hi we are travelling to Japan as a family of four all adult age for the JR pass for 20 days. We realise that a JR pass is useful for the parts of our trip where we travel to and from Hiroshima and Kyoto. However we also plan to go into the Japanese Alps for a week and we are trying to work out if it is better value for money to hire a car and pay a drop off fee or to use a JR pass for 21 days.

Our current itinerary has arriving on the 22nd of September at Narita and we thought it would be best to pay for the fares to Matsumoto 23rd Septand then use a hire car through the alps for a week until we get to Kanazara then activate a 14 day pass when leaving there? We would then travel to Kyoto, Hiroshima etc Can you please advise