If indeed it was rented (where can you rent a PC-12?) the estate of the pilot, along with the pilot's family, will likely sue the owner of the aircraft, along with the manufacturer of the aircraft and any entity that made anything that was on the aircraft. Ultimately, though, if there were only 12 seats and 17 souls on board, the pilot is at fault, regardless. It is his sole responsibility to ensure that everyone on the aircraft is belted in prior to take off and that clearly can't happen when you have 12 seats and 17 people on board. This one will be in the courts for years and years and the only winners will be the lawyers....
From the article:
The aircraft involved was owned by Eagle Cap Leasing, of Enterprise, Ore., and had reportedly been rented.