how many days pass shd i buy

'we are a family of four travelling in japan for a 15 day holiday. we will travel from odiwara to kyoto on 29th July and then from kyoto to Osaka on 31st July and then back from Osaka to Tokyo on 6th August. In between we will be travelling between Osaka and Kyoto. How many days JR pass should i buy?'

Does it make sense to buy a 7 day JR pass activate it on 29th July and then buy a separate pass for the return from Osaka to Tokyo on 6th August, or should I get a 14 day Pass.

Which option would be cheaper?