how I would do it is to use an app that can bulk export from G drive to a local folder on the tablet. then set up moon preferences to auto import that folder to shelf
I use folder sync- but as you only need to do it once, any file explorer type app should work
https://play.google.com/store/apps/d....lite&hl=en_GB
alternatively, if you can browse to your google drive from within Moon ( files tab) it will open the books directly from there, one at a time , as you read them. All it will store locally is a database of covers, book details, read progress etc. it will not need to make copies of the actual book files
I know that method works with dropbox - I can browse all my dropbox fiolders from within moon. I have not tested with google drive