Jason Barrozo, 22, and his stepbrother Joel, 12, did so while their father Wilson, 42, was sleeping last Wednesday afternoon.
Police said they struck their fathers head with a hard object several times, tied his hands and feet and then dragged him a few meters away from their house in Sitio Baloquing in this towns poblacion.
Then they poured gasoline over his body and set him on fire.
Jason and Joel escaped after the incident and are now the subjects of a police manhunt.
Sonia Hipolito, Wilsons common-law wife, told radio station dzSD in an interview that Jason and Joel apparently took revenge on their father for beating them whenever he got drunk.
She said Wilson, a fisherman, spent his money in drinking sprees, while she and her children eked a living by selling vegetables and candles near the church in this pilgrimage town.
Sonia related that Wilson sold Jason, when he was a baby, to a woman in San Carlos City. Jason was Wilsons son by his first wife, a certain Teoding.
Teoding, according to Sonia, searched for Jason and when she finally did find him, she had to pay the San Carlos woman to get back her son.
When Jason turned 10, Sonia said Teoding told him that his father (Wilson) lived in this municipality.
After a long search, Jason finally found his father. He, however, was saddened to discover his cruel ways.
Sonia narrated that Wilson once put their one-year-old baby in a sack and threw him under a mango tree. He was incensed when the infant defecated on the sleeping mat.
Sonia admitted that Jason intimated to her that he wanted to give his father a lesson. But she said she advised him against it, saying he might kill his father.
At about 4 p.m. last Wednesday, however, while she was taking a bath in a friends house, Jason and Joel executed their plan.
Sonia insisted though that the two were not high on drugs when they killed their father.