DonAntonio, your theory corresponds almost exactly with my own theory.
Only variances,
The hit-team could have stayed in a residence on a short-term rental basis. Many such units are available in Toronto, (some possibly even walking distance from the Sherman home) but much harder to trace than traditional hotels and motels.
The hit-team would likely have used burner phones or similar devices that were basically untraceable.
The staging of the bodies was likely done at the request of the employer(s) of the hit-team.
MOO
I'm on the imported hit-squad team as well.
Two or at the very most three came to Toronto from abroad with some kind of fairly reasonable cover story. Christmas in Canada? It's a better cover story than the Skripal poisoners saying they wanted to see Salisbury Cathedral. Maybe a business meeting? Although a short-term rental of a house or a townhome means more of a paper trail, there will be fewer cameras and less overall security than in a hotel. Question: I prefer hotels to VRBOs, so I've never rented the latter. Do you need provide passports/ID or just a credit card?
IMO these guys are foreign nationals procured through a shady security contractor. I think they have state-sponsored training (military, GRU, CIA, Mossad, etc.) in covert action, evading security, and yes, assassination/wetwork/whatever you want to call it. No, I do not think that these guys were actually employed by such an entity--just that this was their background. I think there have to be at least two. Their victims were seniors but not entirely frail or vulnerable. They couldn't be sure in advance whether they would both have to be dealt with at the same time, and I don't think they would take chances.
I know that often strangling is characterized as an an intimate way of committing murder, thus indicating a personal motive, but here, I think it shows the murderer wanted something quiet and efficient that leaves minimal forensic evidence. Strangulation is not "quiet" in some senses, because it takes the victim some time to die, but unlike stabbing or bludgeoning it's harder for the victim to make noise, and unlike a gunshot the sound is not likely to carry outside the house. Someone who uses strangulation for this kind of murder has to be very confident in their physical strength and skills. As for the staging as M/S, I don't think the contractors thought that the LE would seriously consider M/S for very long, but maybe for long enough to cause delays and contamination of the scene and evidence, and to get out of town.
One of my questions in this scenario is the date when the murder was supposed to take place. Was it scheduled for a specific day or were they just looking for a window? I know Kevin Donovan has indicated his belief that the person who procured the contract was there when the murders took place. To me, that seems all wrong with what I perceive to be the financial motive. I think the procurer would want to be as far away as possible, say, on another continent. So how long were the killers watching the Shermans to find the right time? Surveillance would would require different vehicles. I wonder if LE has looked at car rentals. Like, say, three guys at the same VRBO address renting a car each for a week or two? Vehicles that are nondescript yet not out of place in a wealthy neighborhood?
JMO only. In a lot of cases that I follow, I have come down to earth and adopted more mundane theories. This is one where I truly believe that the truth is fictive.