Read only settings

[Lyons Sandstone]

I have a small office with 4 computers including 1 server. All documents need to be accessible by all workers on all computers. My problem is that every time a document is created on one computer, even if it's first save is to the server, no one else has read write privileges on it until we have gone to the server and set privileges to all read write. Why is this and how can I change it such that documents are automatically set to everyone read write? I am working on Macs.