"I feel sorry the brothers have hurt each other with such a bizarre lawsuit. I never taught them to hate each other," On Suthison, 67, mother of defendant Yuthaphum Madnok, 36, and Thanawat Madnok, 37, told the Bangkok Post when she attended the court hearing Tuesday.
Mr Thanawat filed the lese majeste complaint against his brother in May 2010.
The prosecutor last September indicted Mr Yuthaphum on two counts - making defamatory comments about members of the royal family while watching television, and writing insulting words about the monarchy on a compact disc.
"He [Mr Thanawat] thought I loved Yuthaphum more than him so he never really helped his younger brother who in fact gave financial support to the family," the widowed mother of three said.
Mrs On said her younger son was straightforward and kind, while the elder son was quiet and might have harboured ill feelings against his younger sibling.
Mr Thanawat testified to the court that Mr Yuthaphum was belligerent, outspoken, stubborn and disrespectful. He said they clashed when their dogs fought and Mr Yuthaphum often held parties at the house.
He said that in May 2009 he heard Mr Yuthaphum making insulting remarks about the King and also saw him writing rude words on a CD. Mr Thanawat said he had always been a good son, working hard to pay for his university studies until he graduated.
"But Yuthaphum always misbehaved, drank and did not abide by rules," he said. "I helped him when he was charged [by police] with swindling people but he still behaved belligerently."
Jongkol Kongthin, Mr Yuthaphum's wife, said her husband collected money for the family business and delivered it to Mr Thanawat but he was always reluctant to give any money to her husband.
Ms Jongkol said they usually quarrelled about their dogs and business matters.
Mr Yuthaphum said his elder brother filed the complaint against him when Mr Thanawat was kicked out of the house and after he registered a new company and began running it without him.