They had previously pleaded guilty to second-degree murder.
Prosecutors and Silliman's family asked for the maximum sentence.
"Aadil Kahn and his fellow perpetrators should receive the longest possible to sentence to ensure us the safest possible community," Silliman's father Ben Silliman told Superior Court Judge Paul Ridgeway.
Sheriff's investigators found Silliman's body on the bathroom floor of an empty mobile home near New Hill in southwestern Wake County on December 3, 2008. According to the medical examiner, the Eagle Scout was drugged and suffocated.
He was found zipped into a sleeping bag, with his hands and feet bound with plastic zip ties and a bag over his head.
In September, a jury found 19-year-old Ryan Patrick Hare guilty of first-degree murder and murder conspiracy in Silliman's killing. He was sentenced to life in prison. Prosecutors said Hare was motivated by jealousy because Silliman was romantically involved with Dalhquist - Hare's on-again, off-again girlfriend.
Both Dahlquist and Kahn agreed to testify against Hare at his trial in exchange for lesser charges, but only Dahlquist actually appeared in court. A judge later ruled Khan could keep his plea agreement even though prosecutors said he stopped cooperating.
In court Monday, Silliman's father said Kahn lied to him when he asked if he knew where Matt was.
"Aadil knew Matt's parents better than the other two perpetrators yet consistently he lied when asked for Matt's whereabouts," said Ben Silliman.
Both Kahn and Dahlquist apologized to Silliman's family in court.
"I don't expect you to forgive me, but I want you to know that I'm sorry," said Dahlquist.
The fourth defendant - 18-year-old Drew Logan Shaw - entered a plea Monday to accessory after the fact to second-degree murder. Like Dahlquist, Shaw testified against Hare. However, he did not have a plea deal going in.
Judge Ridgeway sentenced him to 45-63 months. He's already spent two years behind bars.