Frank Carberry, 54, once an enforcer for Glasgow crimelord Arthur Thompson, turned up at stables in Lancashire with daughter Nekole Carberry and shouted: "I've come for my horses. You've got my... horses."
After kicking a locked gate open at the riding school, which is around 35 miles north of Manchester, he hit his victims with a walking stick while his pregnant 27-year-old daughter struck one of the men with a chain.
Carberry, of Erroll Gardens, Glasgow, was found guilty of three charges of common assault at Blackburn Magistrates Court, while Nekole Carberry, of Wallace Gate, Bishopbriggs, was found guilty of two charges of the same offence.
The court heard the tenants of the stables had recently forfeited their lease, owing £82,000 in unpaid rent. Several horses remained at the stables and were being looked after by estate staff who were helping owners collecting their animals.
Martin Sutton, a retired detective inspector with Greater Manchester Police who was working at the stables, was attacked after he came to the assistance of handyman Stephen Orrell, who was screaming for help as he was being assaulted.
Mr Sutton said: "I realised that something was wrong and I saw them coming towards me. The man asked me who I was and what I was doing here and then, before I could answer, started to hit me with his walking stick. He hit me three times and then he pulled out a knife and started slashing it through the air four or five times. It was a vicious and unprovoked attack."
Chris Hidderley, a stable hand who also gave evidence at the trial, said: "We had heard the night before that the Scottish Mafia were on their way down but that was just a rumour."
Carberry, who once attempted to join the national executive of the British Show Jumping Association, was sentenced to five years in prison in 2006 for sexually assaulting three young men, including one at a Horse of the Year event. The father-of-five had admitted to being gay at his trial, but claimed: "I don't have sex with boys."
In 1995, he was fined £500 for assault after he threw a horse's ear at a female victim in Lenzie. Three years later, he was banned from showjumping for three years after he punched a man at a horse show.
Carberry and his daughter are due to be sentenced next month.