ALLAN DU YAPHOCKUN, ALFREDO HEBRONA, JR., ROGER C. PARE, GENERAL SANTOS CITY-SARANGANI REAL ESTATE BOARD (GENSANSARREB) AND SOUTH COTABATO REAL ESTATE BOARD (SOCOREB), PETITIONERS, VS. PROFESSIONAL REGULATION COMMISSION (PRC), PROFESSIONAL REGULATORY BOARD OF REAL ESTATE SERVICE (PRBRES), AND PHILIPPINE INSTITUTE OF REAL ESTATE SERVICE PRACTITIONERS, INC. (PHILRES), RESPONDENTS