They had fled across the border to Bangladesh amid heavy fighting between the Myanmar military and rebel insurgents in Rakhine
Speedy Trial Tribunal Judge Anup Kumar handed down the verdict on Wednesday in the case over the killings in 2014.
The assailants murdered Aklima Begum and her son Jahid Hossain by cutting their throats with sharp weapons on the night of Nov 24, 2014 following a dispute over land, said court lawyer Entazul Haque Babul.
Abul Hossain Master, Habibur Rahman Habib and Abdur Razzaq have been sentenced to death by the court.
Abul Hossain, the brother-in-law of Aklima, is also the headmaster of Dewla Rani Riverview High School and the organising secretary of Awami League’s Bagmara Upazila unit.