Family First time to Japan for 3 weeks, Which JR Pass to buy!?

Hello!

My family of 2 adults and 2 kids (10 and 12 yr old) will visit Japan for 3 wks in April. Here is our itinerary:

Arrive: Narita to Tokyo, plan to take limo bus to hotel
Day 6: Tokyo to Kyoto
Day 11: Kyoto to Osaka
Day 15: Osaka to Hiroshima
Day: 17: Ferry to Miyajima
Day 18: Hiroshima to Tokyo
Day 21: Depart Tokyo from Narita

Which JR Pass to purchase? Would 14 day or 20 day be best? Would we still need a local card like Suica? Any tips and advice is much appreciated! Thank you so much!