Kindle e-Ink:
Download book from JNC. Run Calibre. Click add book to library. Attach USB cable between PC and Kindle. Click send to device. Device > eject. Done!
Kindle to Fire android tablet:
Uhhh ... sorry. Calibre can convert to kindle format if you want to use the Kindle app instead of an EPUB reader app, but I've never done this. The EPUB apps I checked in the Kindle app store mostly had negative reviews, this is where not having the Google Play store hurts.
You can also use Calibre's built-in ebook reader to read it on the PC.