Garon Jewell, 19, and Draven Jewell, 21, are accused of killing 23-year-old Max Maguire in the fight outside the club in Lymington, New Forest.
Jurors at Winchester Crown Court heard the younger sibling became ‘rude’ when questions were asked about his age.
Two friends of the victim, Georgia Hole and Luke Gray, were also stabbed during the altercation.
It happened just before midnight on October 22 2021.
Adam Feest QC, prosecuting, told the jury the two defendants were among two groups of people drinking at the private members’ club who loosely knew each other.
He said tensions rose in the garden area after Garon Jewell was ‘rude’ to Mr Maguire and Mr Gray, after they had asked how old he was.
The prosecutor said another cause of the disagreement between the groups came after Ms Hole’s partner, Thomas Dunn, asked if he could buy a nitrous oxide canister, known as laughing gas, which Draven Jewell had found earlier and had brought with him.
Mr Feest said the younger brother then called Ms Hole’s mother, Rebecca Wort, a ‘whore or a slut’ as he left when staff cleared the club at closing time.
The prosecutor said the violence outside lasted about 20 seconds and added: ‘Max Maguire died within moments from a wound he received to the left side of his chest, a knife wound.
‘This had penetrated his lung and damaged a major artery internally and caused catastrophic and non-survivable injuries.’
Mr Feest said Mr Gray, 23, suffered two serious wounds to his lower back which required emergency hospital treatment.
He added that Ms Hole, 23, suffered a less serious injury to her chest.
The court was told that Draven Jewell was captured on CCTV dropping a chef’s knife and picking it up again as he entered the club.
Mr Feest added the older brother caused the fatal injuries and the wounds to the other two victims with the knife, but his brother was ‘jointly responsible’ for the violence.
He said Ms Hole described the defendant with the knife ‘swinging it round like a wild animal’.
Crying could be heard from the public gallery as CCTV of the incident was shown to the jury.
Draven Jewell has pleaded guilty to possession of an offensive weapon but, with his brother, denies murder and an alternative charge of manslaughter of father-of-one Mr Maguire, from Pennington.
The older defendant also denies the attempted murder of Mr Gray and, with his brother, two alternative charges of wounding Mr Gray.
Both brothers, from Lymington, also face two alternative wounding charges relating to Ms Hole.
They claim to have acted in ‘lawful self-defence’, the court heard.
Mr Maguire’s family said in a statement released through Hampshire police: ‘Anyone Max ever met fell in love with him instantly.
‘He would have you in tears of laughter.
‘With a heart of gold, he would help anyone in need.
‘Max was an amazing father to his beautiful daughter Delilah Daisy. Her father has been robbed from her.’
The trial continues.