10 days trip

Hi! Good afternoon! Me and my family are traveling to Japan at the end of next month. I just have a couple of questions please. But first here is our itinerary so far this is not yet complete but these are some of them. there are 6 adults and 9 children.

6 nights Tokyo
4 nights Osaka
We will be staying in Shibuya for 6 nights.
So we are planning to be visit Disneyland, Asakusa, Ueno Park, Sky Tree, Chureito Pagoda, USJ, Kyoto, etc.

1) Is it worth it to buy JR Pass for each passenger for 10 days?
2) Is there JR lines to all these places that we want to visit?
3) Children and adults have the same price for the JR Pass?
4) Can we use the JR Pass also for buses and convenience stores?
5) The price that we will pay are for the days we are going to use it NO need to top up?
6) How do we know if the line is JR line or not?
7) Can we use the JR Pass from the airport to Shibuya on the day that we arrive?
8) Can we use the JR Pass from Osaka to Kansai airport on the day that we leave Japan?
9) Once we leave Japan is the JR Pass still be valid if we want to go back to Japan in the future or do we have to buy another pass?
10) What are the limitations of JR Pass? Are there things we need to know before buying this?
11) Can we have a list of places that we can JR Pass?

That is for now, hoping for you kind response. I will be waiting. Thank you so much!

Dawn