BuddyPress.org

There is a config file setting that will allow you to run BP on all of your user blogs… so you could run BuddyPress on as many sub-domains as you wish. I have no idea how you might run one instance on multiple fully qualified domains however. That doesn’t sound possible to me. But I’m no networking guy.

define ( 'BP_ENABLE_MULTIBLOG', true );

https://codex.buddypress.org/how-to-guides/changing-internal-configuration-settings/