What are good coop games for tweens on iOS for a road trip?

Eating was one of the few things that got my brother and I to stop strangling each other on road trips. We always had the ingredients in the car to make little cracker sandwiches, and it was our job to make them for everyone to enjoy. Crackers, a block of sharp cheddar cheese to slice, a summer sausage to slice, all stacked and served up on the finest paper towel the back of the van had to offer. Ate up a good half hour or so. Made everyone happy.

Keep in mind that the multiplayer apps will require internet access for players to see each other. Not necessarily. http://ask.metafilter.com/213365/Seeking-twodevice-iOS-turnbased-games or otherwise bypass the need for an Internet connection.

Do they like word games? This is one I learned from a friend, who called it Jado. I've never seen it written up anywhere. It only requires pen and paper (one per player), though I'm sure you could substitute ipads. Each person chooses a secret, 5-letter word. Each writes it at the top of their paper, and folds the top over so no one can see it. I also draw a vertical line down the middle of my paper, to divide it into two columns. In one column, I keep track of my guesses for your word, and in the other, I keep track of your guesses for my word. At the bottom of the page, I write out the alphabet, so I can keep track of letters once I know they're definitely in or out of the word I'm trying to guess. Let's imagine I choose "PAPER." Now, we take turns guessing. Each guess is a 5-letter word. It must be a real, English word. Let's say you guess "WORDS." I write WORDS down on my sheet. I count up how many letters it has in common with my secret word. The only letter it has in common with PAPER is R, so I tell you it has 1 letter in common. I write down a 1 next to WORDS. (On your paper, you also write down your guess, and the 1.) Now it's my turn to guess. I guess "MOUSE." You tell me it has 0 letters in common with your word, so in the second column on my page, I write down MOUSE and 0. Now I can cross out M, O, U, S, and E from my alphabet, because I know none of them are in your word. Double letters count individually. So if you guess APPLE, it has 4 letters in common with PAPER: A, E, P, P. (Each P counts as one.) But if you guess APING, it only has 2 letters in common with PAPER (A, P), because only one of the P's is matched. And you keep going until someone correctly guesses the other person's word. Also, you have to guess the actual word, not an anagram. An anagram would have 5 letters in common, but you still haven't guessed the word yet. One guess per turn.

https://itunes.apple.com/us/app/forbidden-island/id427419772?mt=8 - and they'll be on the same team!

Oh my, Spaceteam! I got introduced to it at a family gathering by some college age cousins, and it was a ridiculous amount of fun. The cousins playing it ranged from 18 to 45, but it's absolutely fine for tweens. Strongly seconded. And yes, it will be loud. Ticket To Ride has a multiplayer/pass the iPad mode, and they should be around old enough for it.

What about audiobooks?

http://en.wikipedia.org/wiki/Jotto is my favorite word game ever, perfect for two players and long trips, and not enough people know about it. The gist: each player picks a secret word of 5 letters and keeps it in mind ("MOUSE"). The other submits guesses one at a time and is told how many of the letters match up ("HOSES?" "Uhh... three"). Take turns guessing until someone gets it.

Do they like Scrabble, Bananagrams, etc. ? If so they will probably enjoy playing Words with Friends together on their iPads.

http://www.scpr.org/blogs/newmedia/2013/05/30/13843/ok-go-releases-an-iphone-game-that-has-nothing-to/