How can i date thiz person?

thiz boi i really like i've been liking him for awhile now? we r friends an his sister iz my best friend.. we get along very well .. how can i tell him how i feel about him?? i want to be wit him but at the same time i dnt knoe how to tell him an when it comes to his sister i dnt knoe how to tell her to??b-cuz they have thiz rule where they can't date each others best friends!! so wat should i do???