This is not porno, it's theatre. You have to be actors, improvising around a scarcely sketched script, with skill and patience. Taking on an edgy subject and playing it thru to the end. Or maybe you truly are half-siblings and you've come to terms with the emotional reality: fuck the conventions, there's only one way our feelings can express themselves. If that's the case, you are amazingly courageous. And fair. And why the hell not?