Hierarchical MUC Refactoring

We are trying to refactoring the ejabberd mod_muc in order to handle a sort of hierarchical MUC:

"rooms will be hierarchically related, so the user logging in one room will be visible in the ancestors rooms and will see users presence from the descendants rooms"

This is the main concept.

Practically, when a user is logging into one room, must send presence stanzas to the ancestors rooms, and must receive presence stanzas from the users in the descendants rooms.

Which are the mod_muc functions sending presence (available and unavailable) stanzas to the logged users?

How can I retrieve the list of logged JIDS given a room JID?

I am studying the mod_muc source, do u have some suggestions? Is it feasible do do it?

Thanks

Alexej, Italy