Can JR pass be used in the shinkansen?

Hi there

We plan to take the shinkansen from Tokyo to Hiroshima and on to Fukuoka, then back from Fukuoka to Tokyo in May 2020.

1. Should be get the JR pass to use the shinkansen for the above trip? Does the JR pass cover it? Would it worth to get the JR pass or just single ticket?

2. Do we need to book a seat for those trips? We think it is hop on hop off with the JR pass but we may be wrong.

3. We do not plan to stay in Hiroshima, just stop by. But we cannot be sure if we have time as we were unable to search shinkansen info for those trip.

Thanks