Okay, why didn't they turn around, even ram the other vehicle?
I don't think that they were kidnapped at gunpoint at the location of the truck because almost no part of that scenario makes sense to me including an apparent lack of motive by anyone who would have been likely to make contact with them. That doesn't mean it didn't happen, and I respect the opinions of those who believe that this is a likely possibility.
However, I believe that the Jamisons could have rammed a hypothetical vehicle in front of them, or they could have backed up, or maybe they could have crowded around the vehicle in front of them, but I don't know that they could have easily turned around. The hypothetical vehicle could probably have gone around the Jamisons onto the location to turned around or it could have backed up. If LE was able to get past the Jamison truck, it seems logical that the hypothetical vehicle could also have done it, but this doesn't mean that the road was wide enough at the location of the hypothetical vehicle for the Jamison's to go around it.
I suppose that if Mr Jamison just thought there was a misunderstanding with a nutty neighbor carrying a gun he might have exited the truck alone to try to reason with him. If Bobby believed that the hypothetical kidnapper was likely to shoot or kidnap them, I'm pretty sure that there would have been a lot of ramming, spinning, backing, passing, shooting and anything else he could do to avoid having his family killed or kidnapped. If Mrs Jamison had seen a hypothetical kidnapper pull a gun on any of her family I'm thinking that she would have used her pistol (leaving casings if it was a semi auto) and probably not bothered to lock up the truck as she exited it.
If the Jamisons got into another vehicle at the location of their truck, I'm pretty confident that it was of their own free will although it could later have turned into a murder, if the hypothetical kidnapper learned that Jamisons were carrying a significant amount of money. Maybe another poster who believes in the kidnapping at gunpoint at the truck scenerio can come up with a logical way this could have happened.