Although police have said that this is a triple abduction, part of me is wondering whether, somehow, the grandfather decided to skip town with his grandson. If that were the case, then it would be very carefully planned with an extra vehicle, all the money put in a separate account perhaps under a different identity, and travel outside of the country before anyone knew that something was wrong.
What I means it that if this was a random/robbery/attack/abduction, then there's really no reason to remove a body from the house. It almost seems that one body was removed and two other people left ... all in a vehicle that was not registered to the family or the residence. There was mixed information about where they were going, and perhaps that was deliberately done by the grandfather to confuse everyone about where he would go after everything was liquidated. I'm thinking that if all the assets were liquidated, then there was a lot of money that had to be shared by two people, but one person might have thought that it would be a more comfortable lifestyle if the money was for one person.
The only reason that I can see for abducting either parents it to force them to hand over the assets/money.