Maming Bin Mama, 21 and Sagrueara Jaehsea, 25, confessed on Monday to gunning down the brothers --aged three, five and nine-- as they returned home from a local mosque in Bacho at the start of February.
The men also shot the boys' mother, who was pregnant, although she survived the attack.
The district is among the most volatile in Narathiwat province -- one of three Muslim-majority southern provinces blighted by a decade-long insurgency which has claimed around 6,000 lives.
Police said the rangers carried out the attack after the boys father allegedly shot dead Mamings brother and sister-in-law last August in the same district.
The father was arrested but later released with insufficent evidence to prosecute him.
"They (the rangers) confessed that the killings were motivated by revenge," provincial police commander Pattanawuth Angkanawin told AFP, adding the men gunned down the children by accident as they tried to kill the father -- who escaped unharmed.
Another suspect was still at large, Pattanawuth added. The two men remain in custody.
Rebels blamed Thai authorities for the boys murder and several Buddhists were killed over the following days in apparent revenge, including two women, a monk and a nine-year-old boy.
The bodies of both women were set alight and notes left at the scene saying the attacks were punishment for the death of the brothers.
Shadowy insurgents are fighting for a level of autonomy for the south from Buddhist-majority Thailand, which annexed the region more than one hundred years ago.
The roots of the insurgency draw on long-standing anger at efforts by Thailand to assimilate ethnic Malay Muslims and at a perceived lack of respect for local language, religion and customs.
The majority of the dead have been civilians, caught between warring rebels and Thai security forces, who rights groups accuse of acting with impunity.
Peace negotiations between some rebel groups and the Thai state raised hopes of a breakthrough in the bloody conflict, which has seen a recent spike in violence.
But the talks have stalled, with the Thai government failing to respond in detail to a list of rebel demands while it handles political turmoil in Bangkok.
The Malaysian official facilitating the talks said despite a "temporary suspension" there was still the will on both sides for peace contacts to continue.
"This dialogue process is still in an embryonic stage... no formal talks between the two parties could be held (since June) because of the temporary status of the caretaker government," Ahmad Zamzamin Hashim said last Friday in Pattani.
But he expressed hope for an eventual ceasefire with a new rebel group also poised to join the peace process and Thailand now recognising the need for a "political solution" to the conflict.
Editor: Ade P Marboen
Copyright © ANTARA 2014
