Luke Sandlan, 27, and his brother Elliott Sandlan, 21, stood side by side in the dock at Preston Crown Court as they were sentenced for the savage attack in a crowded bar at the Pier Jam Festival in North Shore, Blackpool last year.
The victim suffered at least 14 stab wounds so severe he went into cardiac arrest while he awaited medical help.
It is feared he may lose a leg after multiple operations to try to repair nerve damage and circulation.
Recorder of Preston Judge Mark Brown QC said: “This must have been an appalling incident for those who witnessed it. What took place was a sustained and ferocious assault upon (the victim).”
The court heard the brothers, of Boddington Road, Eccles, Greater Manchester, had travelled to the resort to attend Pier Jam on September 26.
While in Blackpool, Elliott had bought a knife – from a novelty shop on the seafront – which his brother Luke had taken off him.
During the course of the evening there was a row between the victim and Elliott in which the victim threw a bottle and threatened Luke, the court heard.
Moments later, the brothers ran into the Sunset Bar wielding fire extinguishers and launched the vicious attack.
As Elliott discharged the fire extinguisher, spraying foam across the crowd, Luke lunged at his victim with the knife he had taken from his brother. Horrified revellers and security staff described seeing the men kicking the victim while he was on the floor, and one man hitting him with a fire extinguisher.
When paramedics arrived at the bar at around 10.45pm the victim was fighting for his life as tourniquets were applied to his arm and leg in a bid to save him.
The brothers were identified during proceedings on September 29 and were arrested.
Luke pleaded guilty to attempted murder and possession of an offensive weapon, and Elliott admitted wounding with intent.
The court heard neither of the men have extensive criminal records.
Judge Brown said: “This was a group attack.
“The attack was sustained and a large number of stab wounds were inflicted.
“The events took place in public in full view of a large number of people who must have been extremely distressed by what they witnessed.”
The victim was taken to Royal Preston Hospital where he remained for a number of weeks undergoing treatment for stab wounds to his legs, abdomen and shoulder. He said he remembers nothing of the night after seeing a man with a fire extinguisher.
Elliott was jailed for seven and a half years with an additional two years for supplying class A drugs to an undercover officer.
Luke was jailed for 11 years with 18 weeks of a suspended sentence activated and added to his sentence.
The pair had also been charged with attacking two other men at the event, with both taken to hospital suffering from single stab wounds.
The court accepted these charges will lie on file.
Det Insp Gareth Willis, of Blackpool CID, said: “This was an extremely serious incident which but for the intervention of medical staff would have resulted in a fatality.
“One person has been left with life-changing injuries.
“More than 2,000 people attended this event and we are extremely grateful to witnesses who came forward to assist in the successful prosecution of these offenders.
“I would also like to make special mention of the security staff at the event who were directly involved in the apprehension of the offenders as they attempted to leave the scene.
“We appreciate and understand the majority of people want to enjoy themselves at music festivals and do so in a responsible and appropriate manner.
“However, there was no excuse for the deplorable actions of either man and we welcome today’s judgments which should serve as a warning to others.”