Android Sync to OFB or SharePoint

We have a need for two or three dozen people to share and sync files. They are often in places with no internet access so the sync is necessary so they can makes changes to their files and, when they connect to the internet, have the files synced with others.

If the users had Windows 10 tablets it would be easy. We would create SharePoint sites and sync with the OneDrive client. However, most of these users have android clients. 

Is there an android sync client for SharePoint or OFB? 

If not, can anyone suggest an alternative?