Also, read the very first post at
https://www.mobileread.com/forums/sh...d.php?t=283371
This is the solution I have implemented. I run Windows 10 x64, my wife has an iPad as well as other family members and some have Android devices. I use Calibre on the PC to manage my 17,000 ebook library, I get the free books from Amazon for the Kindle (download the books, store in Calibre, see the post referenced above). My wife used Marvin3 on the iPad as well as other family members. On the Android I'm lost, my Samsung Note died and I have not replaced it at this time, still trying to determine what I want/need. I mainly read technical books, my wife reads mostly the big popular authors. Other family members, it varies greatly. I listen to a lot of audiobooks on my Android phone which utilizes MP3 files.