15 Day Itinerary

Hello there,

A 7 day JR Pass would offer great value for the above itinerary, especially since you both visit Hiroshima and Tokyo.
You could activate your JR Pass either on day 1 or day 2. You can use the JR Pass for travel from Kansai Airport - Namba but you could also consider activating it on day 2 and use it on day 8 to make a day trip from Tokyo. Either way works.

Seat reservations are recommended for longer distances, such as Kyoto - Tokyo. As it will allow you to just go to the train and take your seat without having to queue up before hand. Personally I also love the idea that my seat is secure before hand. However it is not required to make a seat reservation, you can just hop on the train when you feel like it and take a non reserved seat.

Hope this helps!
Daniel