Would have been the last area of the interior of the vehicle to fill with water. Front of car would have been canted downward due to engine weight.
Do you know they were buckled? The car was a Mercedes. They are well built and are quiet as far as interior noise. That means they are sealed well. It would have been minutes to fill, not seconds. They most likely knew they were going to drown and yes, at their age and being friends, embracing doesn’t surprise me at all. Sometime Occam’s razor fits. If you think something is up, why aren’t you digging on who they were and why they’d be killed. Old people in sofl fuck up all the time. I used to live there. People die in the canals fairly regularly as well.