Permissions on a small office folder

Hi!

I have a small office, with 5 computers. 3 iMacs and 2 Windows.

My iMac (10.13.2) has a shared folder with the other 4 computers.

All computers have a login (user/password) that i have created on my computer. With all i set to read and write files on that folder.

Every time i create a new file on that folder the permissions are set to me (read & write ), staff and everyone (only read), and not to all the other user that i gave permission to. So, the permissions i set previously dont aply to new files?

Every time a user creates a new file on that folder (mine!) i have to set permissions to my self so i can read or write.

I need this: every time i, or the other users, create a new file on that shared folder it comes with inherit permissions that i set to that folder. Is it possible?

If it isn't, is there any kind of software that automatically keeps permissions set to all files in a specific folder?

Thank you.

João B.