Ahlul Khibra are the experienced scholars in the Hawza who have the full ability to evaluate the standard of knowledge of highest scholars and give scientific opinion about who is the most knowledgeable among all the scholars. They do not need to be Maraaji' themselves. They are not any normal scholar or intermediate students at Hawza.
Ahlul Khibra are the highly qualified scholars in the Hawza. They are known by the majority of the scholars in the Hawza.