@Linkat,
I agree linkat.
you can keep an eye on the older cats, and the others would probably end up spraying the inside of the car.
anyway you slice it, all of them are going to be wound up and miserable.
Aside...I was traveling with 2 cats at one time, just let them free reign in the car.
One of them, Simi, was the type of cat who could see themselves in the mirror, could see stuff on the TV, would hiss at a salt shaker because it had eyes painted on it (a little cat wearing a sunbonnet and gingham dress, of all things...oh, and carrying a basket of flowers) She was a quiet one though.
When we were driving through the Tennesse, every time we drove through a valley, she would stand with her front feet pressed against the window, and scream at the mountain.
Happened too often to be chance. She'd stand there yelling "HEY! HEY MOUNTAIN!"
Then she look at me and scream "DO YOU SEE THIS ****?! THERE'S A MOUNTAIN!!!"
She'd shut up as soon as the mountain back off, so she felt useful I suppose.