Hello and congratulations.
This won't help with 5 cats but I just wanted to share the story!
My cat Jacob used to yowl without ceasing in a cat box in the car, but allowed to be loose in a car we had (a Volvo, it was) where there was a good flat wide arm rest next to the driver, he would sit on that and watch out the front window, occasionally placing a paw on the driver's arm, completely comfortable for any length of journey. Another vehicle that was acceptable had a wide shelf above the glove box, on which he could lie and occasionally touch the driver's hand on the gearstick. Subsequent cars had none of these cat-friendly places, and the yowling resumed, whether loose or boxed, whether box facing forwards or sideways, on front seat or back.
As others have said, once you arrived at your destination he seemed fine, however much he'd yowled en route. With 5, even if you had all the cat-friendly places there could be, the loose-running would hardly be an option, so it's put up with the noise or use drugs.
But blow the rescue remedy for
them -
they'll be fine,
you've got to drive. Ear plugs and rescue remedy for
you would be my prescription!