Hi there , wondering if JR pass will work for us

Hi there, we have our flights to visit Japan for a first time and wondering If JR Pass will work for us , ( wife, me and my 11 yo boy) planning to stay first 3 days in Tokyo next 5 Osaka and Kyoto come back and enjoy the last 2 days in Tokyo , since is 7 or 14 days options for the pass , if I get the 14 days can I get a refund before I left the country on my last day? Or get the 7 days pass and pay the rest of the days individually? Please help , TIA