My almost 5 yr old likes Kiplings Just so Stories (although we've edited out the story about the baby elephant--too much spanking). He also loves the "My Father's Dragon" series, The Mouse & the Motorcycle (b. Cleary) & the Wind in the Willows (a wonderfully long 6 cds!!!) -- although these are a little younger feeling. We've also enjoyed the different story compilations from Barefoot Books. All of these may be OK for your older child, particularly the Kipling & the Wind in the Willows.
We love the language of the classics, but are careful about exposure to violence, so haven't yet introduced the Chronicles of Narnia. But, depending on your children's sensativity, that may hold the interest of both. And 7 books would take you a while to get through! You may also think about the Roald Dahl books (Charlie & the Chocolate Factory, etc) -- again a little too dark for my DS, but my friend's 5 yr old loves them & they're fantastic enough to hold your older boy's interest.
In a completely different direction ~ we've also found some interesting things in the adult-non-fiction tapes. DS is getting interested in space & we found some taped versions of Carl Sagan's cosmos that he listened to on a long drive for hours. This was particularly appealing for DH & I, we get to learn as we drive! We're currently working our way though "A Short History of Nearly Everything". I was surprised how appealing our DS has found these -- Of course, we have to take breaks for questions every so often.
Enjoy your trip

BTW ~ We listen to alot of books on cd & music as a family, but found that, on really long, multiple-days trips, it's was useful for DS to have his own 'walkman' & headphones. Just for those times when we all need a little space from each other...or when Mama & Daddy just can't listen to that particular story anymore. We taped a bunch of story CD's, made mix tapes of favorite music, etc. He has his box of tapes & his tape player for anytime he needs to 'tune out'.