If I was in your place she is so beautiful, cuckolding me would hurt, hurt so good that is. A woman that like her is all a man could ever want, and you give her to other cocks. Cuckold life.
She is beautiful but even thinking of her with guys at all if your her brother is not normal. I have 6 sisters and I don't even thing sexually toward them in anyway. She is a breathtakingly erotic woman.
Very hot but risky. It sounds like she does what she wants . At least she is right up front. She wants him, if she gets her way it may be trouble but, if you want it too, who knows.