Two 16-year-old boys, who allegedly raped two teenage girls at knifepoint in a Rancho Penasquitos park during the Labor Day weekend, pleaded not guilty Monday to 16 felony charges, including kidnapping, forcible rape and sodomy by force.Leonel Contreras and William Steven Rodriguez -- charged directly in adult court -- were each ordered held on $5 million bail.Deputy District Attorney Wendy Patrick said 13 of the 16 charges carry a potential penalty of 25 years to life in prison, making the defendants' possible exposure 325 years to life behind bars if convicted."The nature of the crimes, the duration of the crimes, the number ... the brutality of the crimes, the callousness ... the stranger-rape nature of this offense justified charging them as adults," the prosecutor told reporters outside the courtroom.Ivan Contreras, the older brother of one of the defendants, disagreed with the severity of the charges."The charges they're giving [Contreras] are obviously too much," he said. "How are you going to get him as an adult?"According to law enforcement, the defendants are in the United States illegally, Patrick said, but Ivan Contreras said his younger brother has a Social Security number and is in the process of gaining citizenship.The 15- and 16-year-old girls had been attending a family party in the 12600 block of Spindletop Road and walked to a nearby park about 8:15 p.m. on Sept. 3, police said.The prosecutor told Judge Michael Smyth that the defendants -- both wearing jackets with hoods -- walked past the girls, then came up from behind and immediately ordered them across the street and into a secluded area.The defendants ordered the girls to take off their clothes and took turns sexually assaulting them for 30 to 40 minutes, until family members of one of the girls started calling their names, Patrick alleged."This included every kind of rape you could imagine," the prosecutor told the judge.The defendants threatened the girls before riding off on a bicycle that had been stashed in the bushes, Patrick alleged. As they departed, one of the boys told the alleged victims, "Don't scream, I don't want to have to hurt you," according to Patrick.The girls and the defendants didn't know each other, but Rodriguez lived in the neighborhood where the crimes occurred, the prosecutor said.One social worker told 10News she believes the teens belong in the juvenile justice system."Yes, they should have consequences but these were big mistakes and I just don't think their brains are quite ready to be forever condemned," said Lorraine Barker.A status conference was set for Sept. 19 and a preliminary hearing for Sept. 23.