Our cloud library solution (available here: https://www.kotobee.com/products/cloud/libraries) would be very suitable for you.
There is ebook security so that you can control user access over who gets permission for what. Also there is something called "DRM". This means that for each user (account) you can limit the number of devices/machines that can use this login. This would guarantee that the user is not sharing his login information illegally with hundreds of other users.
For the cloud library solution, we usually give live demos to explain all the features, as it is a very powerful system. If you're interested in a live demo, just let me know, and I'll arrange accordingly with our customer relations manager.
As a prospective user, I'm confused.
How does an ONLINE library address Ceeper's question about how to deliver ebooks OFFLINE?