How about the possibility that the thieves have simply purchased replacement remotes from eBay (or similar), and programmed them when they had access to a compatible vehicle? Maybe the thieves work at a car wash, valet or have organized a larger network of goons (think credit card skimming).
Programming a replacement remote is a simple procedure, requiring only a few moments in the vehicle with the key present... like when parking a car. Paired with an easily accessible address (registration?), you have a crime ready to take place.
This would confirm why multiple vehicles in the same driveway were targeted. Families use the same service providers. It could also make sense of why the "device" occasionally did not work. Maybe they got the remotes / addresses mixed up, the programming did not take or their mule is selling them unprogrammed remotes.
I think this is more logical of a solution considering the facts. Any thoughts?