The Army said two of the soldiers could receive the death penalty if convicted of the crimes, which allegedly took place at Mahmudiya, near Baghdad in March.
One of the two others will likely admit his role and settle the case without litigation, according to his Washington attorney, David Sheldon.
The Mahmudiya case, the fifth involving serious crimes being investigated by the US military in Iraq, has outraged Iraqis and led Prime Minister Nuri al-Maliki to call for a review of foreign troops' immunity from Iraqi prosecution.
According to US military prosecutors, former private Steven Green, who faces charges in a US civilian court, shot dead 14-year-old Abeer Qasim Hamza al-Janabi's father, mother and six-year-old sister in Mahmudiya.
Green then raped the teenager and killed her, and tried to burn the bodies and house to conceal evidence of the crime.
At least two other soldiers raped or tried to rape the girl before she was murdered, prosecutors allege.
Mr Sheldon said Pfc. Jesse Spielman and Sgt. Paul Cortez face the possibility of death if found guilty under the general's order.
Mr Sheldon's client, Spc. James Barker, and Pfc. Bryan Howard do not, the lawyer said.
Mr Sheldon said Barker would "take responsibility" for his actions. He would not say whether Barker would plead guilty.
"It's likely that this case will not be litigated for Spc. Barker," Sheldon said. "He'll take responsibility for what happened and his involvement in it."
Lawyers for the other defendants could not be immediately reached.