Amanda Trottier and Travis Votour were found shot dead on the main floor of their home in January 2014 while their toddler was playing alone upstairs.
Earlier this week police charged three people with first degree murder: Ronald Junior Brazeau, 34, René Samson-Vonrichter, 24 and Sonia Vilon, 39.
Police allege Brazeau is the head of a drug trafficking group operating in the city, and that he ordered the killing after drugs were allegedly stolen from his organization.
Samson-Vonrichter and Vilon allegedly carried out the fatal shooting, said Sûreté du Quebec spokesman Marc Tessier at a new conference Friday.
Six other people were arrested in relation to drug trafficking, Tessier said Friday.
Five homes in Aylmer and Quyon were searched this week and 13 kg of marijuana, four firearms and an undisclosed amount of money was also seized, police said.