On Dec 18, My Dad was diagnosed with a brain tumor in his cerebellum, (larger than a golf ball), He had a?

craniotomy on Dec. 26, The tumor showed to be lung cancer that has spread to his brain. He has tumors in both lungs, 1 adrenal gland, and possibly his stomach,(he is having a pet scan on Monday). The doctors will not give us a prognosis. Please help me understand how long he may possibly have to live. Thank you