For example, if I were to be learning English and science, would I have to learn all the courses of English in the fall and science courses in the beginning of a new year? Also, when you choose a major, do you need to learn all the courses under that category? If I chose business, do I need to learn accounting, marketing, economics, and so on all under that field?
Not familiar with the rules in your particular institution, but in my experience it's simultaneous given limited time and availability. One must still satisfy both a certain quantity of course credit points, and completion of specific base courses. In the case of a joint major, they may find themselves accumulating an excess of credit for the base requirement, depending on subjects' overlap.
I'd estimate it's likely to add an abundance of stress, yet may help with the diversity of your later employment options rather than more immemmorable depth courses (though those requirements may vary; some jobs won't even spare a glance without a master's).