BuddyPress.org

@Bonlu – make sure you have WordPress set up for multisite: https://codex.wordpress.org/Create_A_Network

Then take a look at the recent site wide posts widget (in your wp-admin backend: appearance… widgets)

You need to develop your child theme so that it allows for the widget to be embedded on the home page, or take a look at the code in the widget and implement your own version in your home page template;

Developing your own child theme: https://codex.buddypress.org/how-to-guides/building-a-buddypress-child-theme/