Marqueas Buchanan, 18, said nothing as he walked into a Chester County courtroom Thursday and was denied bond.
About an hour earlier, Clayton Eli Watts, 17, was also denied bond.
Both teens are charged with killing Watts' grandmother. Jimmie Paul, 59, was found dead on her kitchen floor Tuesday night in her home on Williamsville Church Road outside Chester.
The sheriff's office said a third suspect, Shaderius Demark Cohen, was arrested at 9:45 p.m. Thursday in connection with the killing of Jimmie Paul.
Cohen was arrested without incident at 100 W. Lacy St. in Chester, S.C. He was charged with murder and possession of a firearm during the commission of a violent crime.
Channel 9 learned that Paul was shot in the legs and chest in what deputies described as a planned attack and not a home invasion.
Friends of the family told Channel 9 that Jimmie and Mack Paul had raised Watts in their home since he was a young child.
Deputies said neither Watts nor Buchanan had criminal records before this incident. According to arrest warrants, the teenagers had a 9mm semi-automatic pistol and a .357 revolver. Both made statements admitting to the crime, the arrest warrants stated.
When officers arrived on the scene, Watts was sitting in a chair in the laundry room talking with detectives. The victim's husband, Mack Paul, was also speaking to detectives.
Family friends said at the time of the shooting, Mack Paul was behind the house working on his boat that he planned to take fishing this week, and he didn't hear the gunfire.