Membership groups within android app

hello

I am developing an app for my wife's book club. There are 10 members. As a closed group it works just fine. If I launch this on the app store, then everyone who uses the app would be part of the same big list of members.

So I want a way to have groups within this app.

In the app preferences I have a field called clubcode, and the theory is that all the members of the same group would enter the same club code, and get grouped.

My question is this - how to automate? If the first person from the book club downloads the app, it could generate a 4-digit code. They would have to pass on this code to the other members so they all join.

My worry is that this would not be very user friendly. If member #1 gets the app and creates a code... and member #2 does as well - they will not be part of the same group.

The place that i have see this work really well is SUPERBRU - which is a rugby fantasy league system here in South Africa.

Any tips, hints or experience would be greatly appreciated!

thanks!

Alex