So, just a few weeks back we had our summer vacation, which consisted of 14 hours of driving with 4 boys aged 9-15. Needless to say, I'm glad that drive is over. 
Oh man, that sounds awful. I thought the 7 hour drives we did with 3 of us were awful.
Yeah, add another one in and double the time and you'll have our trip. The youngest has ADHD too, so that always keeps it interesting. 
That's rough. I feel for you! But, as you said it's over so life goes on :}
Yeah, I still wake up with cold sweats after nightmares about hearing, "Are we there yet", over and over again. 