Have you asked Google support about your books?
Contrary to popular belief digital books, music, movies, etc. are different than physical books, CDs, DVDs, etc. You do not own them, but have purchased the right to play them. If you had a hard copy book, you could sell it or leave it to an heir. You cannot do the same with a digital book.
Based on the information in your question, it is hard to guess about your video download problem. I would guess that you probably to not have a compatible video player installed.