Membership management system in the hierarchical structure

I want to create a membership management system for a non-profit organization with Spring Boot. And for the authentication and the authorization, I am trying to use Keycloak. There will be parent and child groups, and a user should view other users and group study reports in the hierarchical structure. And a user should be able to create another user and should be able to add that user to their or child groups. And admin users of a group should be able to give some permissions to the new users.
I will store group study reports and financial things dependent on the users in the groups in my database, and I want to keep all users in the Keycloak.
I have lack knowledge, I read community blogs and documentation, but I couldn’t create the architecture. Which topic should I study? Could you advise some issues which I need to dive into?