Nathan and his grandparents have not been seen since June 30, when Nathan's mother left him at their house for a sleepover. When she returned the next morning to pick him up, the three were not in the house.
Police later described their disappearance as a homicide, and said the amount of blood found in the Liknes's house suggested at least one person would have been in medical distress because of a violent crime.
Douglas Garland has been charged with two counts of first-degree murder in the presumed deaths of Alvin and Kathy Liknes.
He is also charged with one count of second-degree murder in the presumed death of Nathan O'Brien.
Despite an extensive search of Calgary landfills, the area around the Liknes's house and a rural property in Airdrie belonging to Garland's parents, investigators have not been able to find the bodies of Nathan or his grandparents.
The service for the Liknes couple will be held at Calgary's First Alliance Church starting at 10 a.m. MT.
A private memorial was held earlier this month for Nathan O'Brien, at which he was remembered by friends and family as a "superhero."