Police originally reported the suspects to be ages 15, 16 and 18. It wasn't immediately clear Sunday why the ages were different.
Morton was charged as an adult, which means he, like the others, would face mandatory life imprisonment if convicted of first-degree murder in Thursday's fatal shooting of 16-year-old Christopher Walker.
Wayne County Prosecutor Kym Worthy asked Cox to take over the case because Brantley's father is a Detroit police officer, Cox spokesman John Sellek said.
The suspects are to be arraigned Monday, Sellek said. He didn't know whether they had attorneys.
