Q. 1. Can you tell me, what is a "postulator?"
A. 1. The "postulator" is a person who presents a case for the canonization or beatification of someone in the Catholic Church.
According to wikipedia, "The person who guides a cause for beatification or canonization through the judicial processes required by the Roman Catholic Church is known as the postulator. The qualifications, role and function of the postulator are spelled out in the Norms to be Observed in Inquiries made by Bishops in the Causes of Saints, which has been in effect since February 7, 1983. A petitioner seeking the beatification may appoint as postulator anyone, cleric or not, who is an expert in theological, canonical and historical matters, and versed in the practice of the Congregation for the Causes of Saints, subject to the approval of the bishop. The major religious orders, such as the Franciscans, Dominicans and Jesuits, appoint members of their orders as postulators-general who are available to act for petitioners in causes and who develop reputations as experts in their field. The later stage of a cause requires the postulator to reside in Rome, which also favors the assignment of the postulator's role to such a postulator-general, since most religious orders maintain their headquarters in Rome.
The first duty of the postulator is to conduct thorough investigations into the life of the candidate for beatification. The postulator also has responsibility for administering funds collected for the cause. Like all officials who take part in a cause, the postulator is obliged to take an oath to fulfil his duty and to observe the strictest confidentiality.
See wikipedia for further information.