Although the confrontation in the bar had nothing to do with him, he was chased along the street with other youngsters - and was attacked and stabbed to death when he stopped running.
Ben was stabbed 11 times in five seconds by the three youths in revenge for a claim that Braithwaite had earlier been "disrespected" the court heard.
The defendants had admitted punching Ben but each denied he was the knifeman.
After the verdicts Mrs Kinsella read a victim impact statement to the court, which said: "We as his family have been left devastated and in total despair. Our whole world has been totally turned upside down."
She added: "We had brought Ben up to always walk away from trouble. This sadly cost him his life."
Sister Brooke said: "There is never going to be enough justice but we have got it now."
After the verdicts, it emerged Kika had been on the run from police following a robbery in which a man was knifed nine days before Ben's death.
George Kinsella: 'We hope that the sentencing will reflect the brutality that was inflicted on our son'
Three other youths were arrested but despite extensive searches and inquiries, Kika was not found until he was arrested for Ben's murder at a flat in Chadwell Heath, east London, on 30 June.
Kika had convictions for cannabis possession, robbery, affray and for restricting or obstructing a constable while Braithwaite had been given a community order for an attempted robbery.
Alleyne was being supervised by the local youth offending team as part of an 18-month detention and training order for drug dealing. He was a convicted cocaine and heroin dealer and also had convictions for robbery and possession of cannabis.
He had been released three months earlier after serving half the sentence in a detention centre.
Speaking outside court, Ben's father George said: "Almost one year ago, our precious gentle son, Ben was brutally murdered on the streets of London.
"How many more families will have to stand outside the Old Bailey to get justice for their child. Our son's only crime was to be the last one, running away, from those animals.
"Knife crime is now sadly embedded in the very heart of Great Britain. Parents live in fear until their children are safely home. It can be for a wrong word, a wrong look, or a wrong post code ....In Ben's case it was simply nothing to do with him at all.
"We are happy with the verdict given and really hope that the sentencing will reflect the brutality that was inflicted on our son."
About 400 people joined the family to march against knife crime following Ben's death.
Alleyne, Kika and Braithwaite will be sentenced on Friday.
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