Get some simple green and a brush you can use on carpet.
Vacuum the seats/carpet and get the loose stuff up. Then dilute some SG in a bucket of water, scrub the carpets, and then vacuum the water up with a wet/shop vac. Pull the carpet out to dry. Dont go too heavy on the seats, you dont want the cushioning to absorb too much water.
You can substitute another cleaner that isnt too harsh for SG, but I cant think of any other then carpet shampoo right now.