Imamah (Divine leadership) is a position granted by Allah to the best of His creatures to lead all human beings to the Way of Allah. Allah tested Ibrahim through many tests and when Ibrahim (AS) completed all the tests successfully, Allah told him: I Am making you an Imam for all people. This Imamah was granted to Ibrahim after he was already a prophet and a messenger. The Imamah of Ahlul Bayt (AS) is the continuity of the divine leadership of the greatest and best and final Prophet Muhammad (SAWA) although none of the 12 Imams was a prophet because there is no prophet after Muhammad (SAWA). The status of the 12 successors of the greatest Prophet Muhammad is from his status and their Imamah is binding all humans as the Imamah of Ibrahim was on all humans. The twelve Infallible Imams are not prophets but their divine leadership is must on all humans.
Wassalam.