Identity parades were held by police investigating missing ewes to reunite them with their rightful owners.
Charles Raine, known as Neville, 66, and his nephew Phillip Raine, 46, were found guilty by a jury at Teesside Crown Court of conspiracy to use criminal property.
Phillip Raine's partner Shirley Straughan, 41, was cleared.
Det Insp Paul Phillips said the 16 farmers who lost sheep had been "absolutely dignified, patient and a credit to their profession".
He added: "Then we have Neville and Phillip Raine, who have destroyed their own reputation and almost been parasites the way they have fed off other farmers around them."
The animals went missing between 2010 and 2013.
More than 115 were identified as coming from farms in County Durham, North Yorkshire and Cumbria, despite usual markers being removed.
Neville and Phillip Raine operated two farms in the Bowes area of County Durham, close to the A66.
They were granted bail and will be sentenced in the new year.
Judge Tony Briggs warned them "all sentencing options including custody" were possible.
Two members of a farming family have been convicted of having more than 100 stolen sheep.