7 day tour from Tokyo to Osaka

Good day!

My family is planning to travel next month to Tokyo to visit some friends who live there and we are also planning a tour around Tokyo for the first 3 days before heading to Osaka on our fourth day. That includes our tour in Osaka, Kyoto & Nara if possible as well on our 5th & 6th day before departing on the next day flight back from Kansai. Is it cheaper for us to take a domestic flight from Tokyo to Osaka or Is it still worth it to buy a 7-day JR Pass before leaving our country?

'viangel