The courtroom is expected to be packed, but the evidence will be protected by a publication ban.
Garland faces two counts of first-degree murder, in the case of the grandparents, and one count of second-degree murder linked to Nathan's death. The first-degree charges indicate investigators think there was planning involved in the homicides.
Garland has connections to the family — he had past business dealings with Alvin Liknes, and Garland's sister was the common-law spouse of Alvin Liknes's son, Allan Liknes.
The victims' families are expected to be represented in court. Rod O'Brien has been present at every court appearance, with Allan Liknes often accompanying him.
Missing: a timeline
Alvin and Kathy Liknes held an estate sale over the weekend of June 27, 2014, in preparation for their move to Edmonton. The O'Brien family was at the home helping out.
On June 29, a last-minute plan was made for Nathan to stay for a sleepover with his grandparents. When his mother, Jennifer O'Brien, returned the next morning, nobody was home. That evening, police issued an Amber Alert.
Police confirmed on July 4 that there was blood found in the grandparents' home and that a violent incident had taken place.
Garland was taken in for questioning the next day and officers began their extensive search of the Airdrie, Alta., acreage he shared with his parents.
Police asked property owners near the Garlands' Airdrie property to search their acreages, looking for anything that appeared out of place.
Police also scoured several fields near Airdrie, sent divers into a pond and spent days at three local landfills.
More than 200 officers were involved in massive searches for the Nathan and his grandparents. Police also followed up on about 1,000 tips from the public but the three were never found.
Since Garland was named a person of interest in the investigation, the community has been searching for answers as to what might have motivated him.
Nathan wasn't supposed to be at the Liknes's home that Sunday night. It was a last-minute decision to have a sleepover at his grandparents' home following their estate sale.
Family and business connections could provide some answers. Garland knows Nathan's grandparents because his sister was in a common-law relationship with Allan Liknes.
There was bad blood between Alvin Liknes and Garland following a business relationship that went sour.
Liknes had previously registered a patent for an apparatus that separates gas from water. Family members confirmed to CBC News the patent was a sore point between Alvin Liknes and Garland.
A junior gas company that was owned by Alvin Liknes, Winter Petroleum, went bankrupt near the end of June, just days before Nathan and his grandparents went missing. It's unclear if Garland had any connection to that business.
Garland`s criminal history includes drug trafficking and possession of stolen property convictions, after he was caught making amphetamines on his parents' Airdrie acreage in 1992.
After failing to appear at court in 1992 for drug charges, the then 33-year-old Garland disappeared.
A document from the Tax Court of Canada indicates Garland was later discovered living under Matthew Kemper Hartley's stolen identity in Vancouver.
Hartley was a 14-year-old Alberta boy killed in a car crash in 1980.
The same document says Garland suffers from attention deficit disorder and had attended medical school in Alberta for one year before suffering a mental breakdown.
Garland told the court at the time he had been traumatized after causing what he described as a horrific accident after falling asleep behind the wheel.
After he was discovered living in Vancouver, Garland returned to Calgary and pleaded guilty to several of the charges in connection to the drug bust and stolen identity, while the others were dropped.
Last year, before being charged with murder, Garland was charged and released on bail for identity theft, again connected to Hartley.
It was days after that he was arrested in a field near his rural Airdrie acreage.
The court process
Though Nathan and his grandparents were missing for two weeks before police laid murder charges, a court document shows investigators believe they died on June 30, the day they were reported missing by Nathan's mother.
A preliminary inquiry gives the lawyers an opportunity to test their evidence.
With no bodies and likely no eyewitnesses, forensic evidence gathered at the Liknes's home as well as the Garland property will be at the heart of this case.
"I like the idea of a preliminary inquiry. It gives us a chance to test drive some of the evidence — make sure where we're at in terms of some of the behind-the-scenes work," said Crown prosecutor Shane Parker in a previous interview.
"It gives us more time to make sure we're ready once the jury trial is slated to go."
Garland's lawyer, Kim Ross, says the case involves the most significant amount of disclosure he has ever seen.
The inquiry is set for two weeks. After that, the provincial court judge will rule on what charges Garland will face at trial.