I did nearly the same thing last year. I picked up day old chicks at the hackery and drove about six hours, spent four days there, then drove another 8 hours home.
The first leg was no problem. The hatchery put a gel heat source in the box, I left the car heat on as much as I could tolerate or a little more. And checked with a thermometer as well as how they behaved. They made a few murmurs but basically were quiet in sound and movement the entire way.
I think there was shipping stress because there was some vibration and turning and braking and I waited until I arrived to start them on food and water. I think the stress was minimized because I drove as smoothly as possible, the temperature was even, it was as quiet as possible, and things like that.
The next leg was much more difficult. At five days old, they did not huddle quietly in a corner. They acted like they had the day before only more so - more running and jumping around, exploring their space. One managed to jump or fly out of their box... I stopped at goodwill to buy a net thingy to cover the top. A solid cover may work for a four hour trip but I didn't want them in the dark for 8+ hours of the day.
They no longer had the yolk available and I didn't want to try messing with their sleep schedule. Or my sleep schedule. So, I stopped to let them eat and drink about every hour or a little less. The 8 hour trip took almost 12 hours.
Anyway. It can be done with minimal stress to the chicks but it takes significant extra time and attention.
I would take them rather than leave them with no more than a typical neighbor checking in once or twice a day. If the neighbor could be trusted to tend to them similar to how I would, I would prefer to leave them.
