James would be the one driving the car because Jessie is lazy and Meowth is too short + he's a Pokémon, plus James is kinda the slave so yeah.
Jessie would be in the passengers seat because it's the best seat in the car and she's kinda like the boss of all three of them.
Meowth would either be in the back seat with the kiddie seat since he's too short to be in the front, or he'd be protected in Jessie's lap in the passengers seat because that's wholesome.
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Cassidy would be in the passengers seat since she's kinda the dominant one in this relationship, just like Jessie, she's kinda in charge of Butch and Butch is ok with the commands.
Butch would be driving ofc since Cassidy is in the passengers seat. He does seem like the kind of person who could easily crash a car tho and Cassidy would be like "HOOTCH WHATZ GOING ON! DO YOU HAVE A LICENSE" and Butch would just say "THE NAME IS BUTCH! AND YES I DO!" He shows a Legoland drivers license...