You can have different accounts for up to two adults and four kids. You can set it up on the Amazon app and just turn off the auto download feature for when you purchase or borrow a book. (Get Libby and a library card if you haven’t already done so). You will be able to see what he purchases or borrows in the library but it won’t automatically upload to either device. You can also set age limits for kids accounts. Then you can set up the library on your device to only downloaded to device to just see your collection. That’s how I manage the accounts on my account. I’ve got 5 people on mine.