Group in shopping list app

Hi I’m really starting on this topic so I would love for detailed explanations

I built a shopping list app and I want to make groups in the app, that everyone who enters a particular group sees the lists saved in the app.

Login to the group will be by a code stored in FireBase.

My question is how to do such a thing and are there any extensions that will help me with that?

One more thing, I need that if one of the users in the group adds a particular product to one of the lists, all the other users in that group will be notified of the addition. Thank you