TORONTO - An Ontario couple accused of killing a man and his mother have been committed to stand trial in their deaths while changes have been made to the charges they faced in the death of the man's father.

Melissa Merritt and her common-law husband Christopher Fattore will be tried for first-degree murder in the deaths of Merritt's ex-husband, Caleb Harrison, and his mother, Bridget Harrison.

Last year, they were also charged with first-degree murder in the death of William Harrison - who was Caleb's father and Bridget's husband - but a judge has discharged Merritt on that count, citing insufficient evidence, and has reduced the charge to second-degree murder for Fattore.

Lawyers for Merritt and Fattore say the pair could stand trial as early as September.

The case is expected to be a complex one, involving an intricate web of family relations.

All three Harrisons were found dead in the same Mississauga, Ont., home over several years.