"Amasa lay squirming in his blood." Amasa may have still been alive and rolling in his blood, but he was probably dead by this time. It is described this way to show how gruesome his body looked. Alternate translation: "Amasa lay dead in his blood" (See: [[rc://en/ta/man/translate/figs-explicit]])
This means they stopped walking and were staring at Amasa's dead body. Alternate translation: "all the people stood still staring at the dead body ... came by him stood still, staring at his dead body" (See: [[rc://en/ta/man/translate/figs-explicit]])