I am having a really hard time figuring out how to effectively set up folder sharing with Windows Server 2012. I have four servers all collocated in a data center. Each server has two ethernet connections, one for access over the internet, and one connecting the four to a local LAN for data transfers and access to SQL data. One of the servers is my dedicated backup machine. I have set up folder sharing on this server but am not familiar with user permissions and how to get this set up correctly.
-I do not have active directory or any other type of user management. The only users set up on these servers are the admin user to login and make changes. Everything else is handled by other applications (SQL Server users, ASP.NET users for web site, etc.)
-I want my shared folder to only be accessible by the servers on the LAN and not accessible over the internet to random people
-I need full read/write access to the shared folder by all machines
With this said, I am not much of a computer administrator. I learn as I go and know just enough to get everything set up for what we need. Think of all the servers as working independent and not connected to a domain controller or anything. I just hit the IP addresses of the services I need. All servers have the same administrator user login, but I'm assuming the servers see these as different since they show up as computername\username. Any help would be greatly appreciated.