Sync a folder on multipe Android Galaxy S7 devices with a server

I need to write an application that allows me to sync a folder on 80 (or more) android Samsung Galaxy S7 devices to a server. I need the Android devices to synchronise and delete content that is not on the server anymore and download content, that has arrived on the server. Since the amout of Android devices is large (80 devices or more), I need the process to run efficiently using resources (bandwidth) in a smart way. The typical size of the folder subject to sychronisation is around 15 GB. To initiate the sync, I need to see all devices that are subject to sync on a web based surface with tick boxes and a command button that pushes the content on selected devices. (see picture attached).