However when you get to a school you will probably find that you will only teach one of them - for the simple reason that you would be in two faculties and that can cause problems - not saying you wouldn't get to teach both just that is it very hard to work in two faculties. Schools rarely need both English and Maths teachers at the same time so you would be put in one faculty and probably only get those classes - e.g. at my school most of our English teachers have History as a second subject and don't teach it because they are needed to cover all the English classes and the HSIE faculty covers all the History classes, same with our Maths/Science teachers many of whom are qualified for both but only teach one due to the need to cover their own faculty and the difficulty of working across two faculties - particularly the big ones like English, Maths and Science - even the fact that you would probably have a desk in one staffroom and have to go to the other to even have a discussion about what you are teaching in that faculty would mean that you would miss the incidental conversations that happen about the subject.
I am not trying to dissuade you but pointing out some of the realities of a school environment and what happens on the ground rather than the theoretical situation of doing that combination.