Thank you very much. I don't know what grade you and your sister are in. That may have a lot to do with this. To prepare your self for RN education, you need to take all of the science and math you can get at your high school. You should get the best grades you can.
Most nursing schools are very competitive.
That is, they have more young people applying for admission than they have room for. These are college entrance exams that the colleges like to see the students take. Your score on these exams can be crucial for some schools and for others they are only used for course placement. You need to research the schools you are thinking about to see if the offer a major in RN, and then see if they are the type of school you like. That is, is the school large or small, private or public, in a city or in the suburbs, and so forth.