Can't open new files in shared drive

I've been stuck with a very frustrating issue after attempting to set up a shared drive on OS X El Capitan server. I have two accounts, one "Sharing Only" account, and another admin account on the server. The sharing only account and the admin account both have full read and write permissions to the shared folder, but when I connect over SMB to the shared drive using the sharing only account and upload a file, I can't open it back on the server.

While it's possible to manually adjust the permissions for each individual file, I can't seem to figure out how to make newly uploaded files from all users viewable to all other users who have permission to access the folder.

Any help is greatly appreciated.