Sharing encrypted image between users on machine

I would like to share this between two users on my Mac. Specifically, I would like the encrypted image to be under user1's Documents directory but allowing user2 to open and modify it. I know that MacOS is a Unix variant. In Linux/Unix I would create a group and add the two users belong that group and make the shared files rw-accessible by that group. I can do this from the command line. Is this the best approach on Mac as well? I was looking for clues under the "Users & Groups" setting under "System Preferences" but I couldn't understand it. There are groups in there that I don't see in /etc/group.