We theoretically study the electromagnetic field controlled photon correlation and radiation properties in a two-atom-cavity quantum electrodynamic (QED) system with different atom-cavity coupling strengths. When two three-level atoms are coherently driven by a probe field and a strong control field, forming a ladder type electromagnetically induced transparency configuration, there exist four different excitation pathways via the two photon processes, yielding four different frequencies for realizing two photon blockades. Carefully choosing the intensity of the control field, resonant single-photon and two-photon excitation can be achieved at the same probe field frequency. Thus, two photon blockade phenomenon can be significantly improved and the collective radiation behavior becomes superradiance or even hyperradiance. Our system presented here can be considered to be a converter of a weak coherent light to two correlated photons.