Yeah I definitely don’t agree about the “none of their business” part. As a parent paying for my kid’s tuition, yes I’d like them to be happy but I should also have a say in what I’m investing in.
To the OP, have the talk with the parents. Maybe you can come to some compromise, like Computational Chemistry or ChemE or a dual major or something like that. Med school is a crapshoot, a low percentage of people get in.