Luciano Aviello and Mario Alessi were among five inmates who gave evidence at Amanda Knox's appeal hearing at the weekend.
She is serving 26 years for the murder of Ms Kercher, 21, who was found with her throat cut in house the two shared. Aviello, 42, who is in jail for Mafia-related crimes, told the court his fugitive brother had carried out the murder after he had been promised 10,000 euros to steal a valuable painting from the house.
Alessi, 51, serving life for killing a baby, insisted Rudy Guede, who has already been convicted of the Kercher murder, told him in a prison yard that Knox and her boyfriend, Raffaele Sollecito,who was also jailed, were innocent.
The appeal was adjourned until next week, when Guede will testify.