Setting Reoccurring Permissions

Hello,

I have multiple user accounts on my iMac, which I am using as a file server over Apple file sharing and SMB... However, I am having difficulties when it comes to permissions.

For instance, I set full administrative permissions for User A, applying these to every file in every folder shared, but User B has access to only one folder. When User B makes changes, adding folders and files, then User A does not have permission, and vice versa.

Is there a way to set more permanent permissions that will apply to NEW files and NEW folders?

Thanks.