I still think the original plan was to come back to move the vehicle and hide/destroy any evidence where the vehicle was parked. They banked on having far more time that they actually did, thanks to, I think it was Jilian's husband? that immediately alerted LE and took off driving down there. A couple of them probably would have taken the car out somewhere and burned it. I suspect a trusted family member was probably with the children while all this was going on because it was a pretty big and risky operation.
I also think that wherever they had hidden these women was not to be the final place. They just didn't have time. As soon as the car was found I'm sure they were all being watched closely and weren't able to go move or doing anything else with the remains.
I am so glad they were caught and Veronica and Jilian will be returned to their families but I am also terribly sad for their loss to their families and everyone that loved them.