Relational database question

In our App, we have a feature that allows multiple moms get connected with each other. Let’s say I have a mom that wants to connect with all the moms in the Soccer group. Mom number 1 creates the group or pod and invites other moms to this group. We send a SMS text to the Mom number 2. Mom #2, downloads the app and signs-up. When they sign-up, I want to use their phone number to connect her to the Mom #1. However, Mom #2 also can see all the other moms in the Soccer group. I have setup a connected mom collection and Mom #1 is the primary connection. However, I can’t figure out how to setup the Mom #2 when she signs-up based on the phone number and also she can see all the other moms. Any help would be greatly appreciate it.