Which Rail Pass?!

I am travelling with my family, two adults and two children, to Japan in April. We have limitted time, and alhtough we'd like to travel all over, we've sadly had to make the decision to travel in and around Tokyo to make the most of our time, and also a trip to Nakano, Nagano, where my mother is from.

Which would be the best pass to get?! The national... but we're only travelling in and around Tokyo and Nagano, or the regional pass which covers Tokyo and Nagano?! Does the national pass cover all Tokyo lines which we wouldn't get with the regional?!

Any advice would be grately appreciated!!