Is it possible that your parents are moving to the state where the college is located in hopes of being able to pay instate tuition?
As far as dorms go I don’t know if they would allow a male and female to share a dorm space. Usually males are in one dorm room and females in another though there are coed buildings. The only way I would think you could be living in the same apartment is if you both got something off campus together.
I am assuming you are the brother living with his sister.