I have college questions. I wanna get a major in two areas..?

Vet is not a major, and marine bio rarely is. Both require graduate degrees (DVM for a vet, that's 4 years of vet school after college) and PhD for marine bio (4-8 years of graduate school after the bachelors). You'd probably just major in bio and take the pre-vet courses (which you can do at most large universities) and then you can go to vet school or graduate school after college. While you can double-major in two different fields, these aren't majors at most schools.