Adding development users to App Folder application

If you only need to share those files with them, they don't need to approve your app. If you need them to interact with those shared files in your app specifically, then yes, they would need to approve the app to access their account where they have the shared folder. As far as how they authorize the app, I recommend referring to the tutorial for whatever SDK you're using.

An alternative is to use shared links like Steve mentioned earlier in this thread.