Green pass upgrade on tokyo-kyoto?

I will be traveling from April 1 to April 9 as is:
- arriving Narita airport terminal 1 around 12:30 pm on 04/01, going straight to Kyoto - 04/01 to 04/05 Kyoto - 04/05 to 04/06 Nara - 04/06 to 04/09 Tokyo

I am considering getting a JR pass but Since we will be 4, including my mother which is much older, I am not sure if I should take the green JR pass or just ordinary passes, then upgrade to green seats on the Tokyo to Kyoto trip. My main worry is that we would be arriving after a long flight from the US, and I read it could be hard to reserve seats until we actually arrive to narita airport. Since it should be the cherry blossom season, can we still get seats together without reserving ahead of time?

Would it be worth getting a green JR pass or just an upgrade on Tokyo- Kyoto?

I also have more questions:
- how long would it take after arriving and reserving seats to get to rail station? - since the pass only lasts 7 days, can we still get the narita express back to the airport for half price? - I read something about prices could change after April 1st, then does it mean we might need to pay extra fees once there?

It would help me so much if I could me clarify all this.

Thank you!