VoiceDream Reader is the app you want. Zip the mp3 files for each book into one zip file per book, and load the zip files into voice dream reader. It will remember his place, and is pretty easy to use.

the one service that i have had great luck with is Audiable which you can get on most apple products, however MP3 books can be played on most audio players the problem most people run into is that MP3 dont generally save place marks from where the reader has stopped the session

I use a free app called MP3 Audiobook Player. It remembers playback position, has a sleep timer, and bookmark functionality. You just zip the files and transfer them to the app via Wifi.

See if he can qualify for this totally free, but he'd need to qualify and register with his states library fir the blind first. I am not sure if their is an international equivalent if you are outside of the U.S. https://nlsbard.loc.gov/apidocs/BARDMobile.userguide.iOS.current.html