I ended up living with my sister for a week. She's strict with me in front of my brother-in-law, but as soon as he leaves, she starts to get all lovey-dovey and touches my dick. She knows I'm watching, and purposely shows me her sex with my brother, so my dick is rock hard. When I can't hold back and masturbate, my sister suddenly appears and forces me to have sex with her, making me cum every day. The day before she leaves, I enjoy a live-in life with my brother-in-law, having sex while trying not to make too much noise, while sleeping next to him!!