Near end-of-life support. Life support?

My grandfather (77yo) suffered internal bleeding in his brain. A blood clot formed and it went to the part of his brain that's responsible for bodily movement, speech, sight etc. He was rushed to the ICU 3 days ago. Although he has had bypass surgery, his heart is fine. By now, he needs ventilator support for breathing and his legs are jerking sporadically. BP is 140/77. The doctor, after several reports, scans, and diagnoses has concluded that he won't survive and that we can take him off the ventilator and let him pass if we choose to, or he'll suffer the entire time he's on life support. Not to mention the extended financial burden. Is one doctor's conclusion enough to allow us to take off life support? Given that he is not brain dead, and his heart and respiratory functions are working, however weakly so, is it legally safe for us to decide to let him pass? Dead or alive isn't crystal clear, could it count as attempted murder if we choose to take off life support?