Edit: Skip this post. It's just werdz
There are [things] that you can do to make your life easier. Just like on any car you decide to make y our own. And just like cars, you have two options:
1. Buy and make use of what is on the market
2. Build your own
There's a 3rd option and it's a mix of 1 and 2.
The first option is right up the General's alley but the privacy risks are real. You don't use these services for the same reasons that I don't use a lot of these services.
Option 2 isn't even in the same city as your alley.
However, you [know] people that can help with that piece if you decide to tackle it.
My solution if it I were doing it:
You need a small Windows home server that is [on] your home network and [not] connected to the internet. Now, I'm not familiar at all with these Amazonia Tablets that you use but I do imagine that there is a way to make the Kindle backup it's data to a specified location on your home network. If that is true, then you would access this same [private, not internet connected] server with each of your devices when it connects to your home WiFi.
What does this give you? Access to all of your files from every device while you are at home, connected to your home network.
Anywhoo... Maybe you recall that the simulator company hired me to make things [work] together (28 individual computer systems running 4 different operating systems and a dozen, or so, microcontrollers (one of them with a CANN BUS)). *whew* (It was a lot of fun, I can't lie
)