Gang leader gang leader Quynh Van Huynh, 51, was jailed for nine years Monday at Cardiff Crown Court and Thanh Van Le, 31, Cong Van Le, 48, were each jailed for seven years.
It was a case of gangland punishment gone too far, Justice McKinnon said.
Their victim, Tran Nguyen, 44, had been smuggled from Vietnam into the UK in the back of a lorry.
After short stint in Birmingham at a nail bar (such bars offer manicure, pedicure and waxing services), the father of two was sent to a cannabis factory in Keynsham Avenue, Newport, where he became a lone farmer, known as a "ghost."
But within a couple of months when there was a raid on the plant by a rival gang and crop worth Ģ30,000 to Ģ40,000 was stolen. The gang suspected Tran Nguyen could have been a party to it. So they took him away for punishment and thrashed him mercilessly.
The trial heard his wife was telephoned during the ordeal and told by one of the attackers: "Be prepared to collect your husband's corpse."
He was driven back to south Wales and carried into the Royal Gwent Hospital with broken ribs and a head injury by two men who fled the scene.
He died about eight hours later. But his identity was discovered only the following month when his brother-in-law went to the hospital looking for him.
The judge said: "The police officers in this case should be commended for their thorough and painstaking investigation in this difficult case."
In a statement read to the court by prosecutor Roger Griffiths, Nguyen's widow said she feared for her own safety and that of her family after giving evidence to the police.
Pham Thi Thien said: "When I heard the news of my husband's death it was devastating for me and my children.
"You can imagine the situation when a wife loses her husband and children lose their father.
"My husband was a healthy person and he was beaten up to death."
Outside court, Detective Inspector Russell Tiley, of Gwent Police, said that the force was working with the Vietnamese authorities to make sure Nguyen's family was safe and that the police were also looking for another Vietnamese in connection with the death of Tran Nguyen.