Neil Gaimon's Norse Mythology is a really neat audiobook.
If they like horses, go with Rough Magic (a true story about riding in the Mongolian horse race).
And if they haven't ever read Harry Potter, you should absolutely choose to listen to the first book (Harry Potter and the Sorcerer's Stone) above all other suggestions!

If you have Amazon the audiobook Interview with a Robot is good. It’s only an audiobook (didnt start as a regular book) and is well produced.

To Night Owl from Dogfish is another we liked. Two different narrators. I have a boy but these both have female leads and he liked them.

Judge John Hodgeman also fun. Maybe not for 8 hours straight but as part of a mix of podcasts.

We enjoy Bill Bryson’s books on family car trips. I think Good Omans would be good for that age too.

Flipped by Wendelin van draanen is an awesome book.

In terms of podcasts my kids also love Radio Lab, Snap Judgement and This American Life. Not all of the episodes would be fully appropriate for kids, but you could preview maybe or just risk it.

we loved the Harry Potter series on audiobooks - the narrator is amazing

Any suggestions for a podcast or audiobook for family with two girls ages 12 and 14 for roadtrip? 8-10 hours of travel.