In short, at night you could see perfectly into their living room window and their bedroom window even without their bedroom light on and not be seen ...by anyone. You can imagine my interest in that.It was nearing Christmas and they really wanted to go home for the holidays but could not afford it. As with all the other single guys, I knew I would be working through the Christmas holidays so I showed up unannounced at their house one night and gave them money for the trip. They were just stunned,. Krystal laughed and continued with a little more pressure. I leaned my head back against her and just relaxed, revelling in her touch."Penny for them." She said a couple of happy moments later."No thoughts at all. You have me in harmony with the world." I said softly before adding. "Though swapping places does have its merit." I bet it does." She laughed loudly.A few seconds later she surprised me when she said. "Ok then, get up."Slowly, as if in a trance I did. Krystal took my seat and as I. I had never done double penetration but had seen it done. In pictures anyway. Its good that there was already plenty of slickness back there. He started pushing in again. MY ass was on fire in pain. But my own cock was harder than it had ever been before.They start alternatingly pumping in and out of me. It was the most painful thing and most pleasurable thing I had ever felt. It was almost like they had done it before, but they were in a perfect rhythm and it was not long before I was. Don't worry."Later that night I'm lying on my side pretending to be asleep, but actually berating myself for my dirty thoughts. "She's my sister! Not to mention a girl! I-I'm not a l-lesbian. I sigh and try to get some sleep. I close my eyes and start drifting off. My mind a confusing jumble of thoughts.When suddenly I hear my sister making strange moaning sounds in her sleep. "Karin". I sit upright at hearing her moan my name. "she isn't! Is she?" About me? My mind thinks back to her panties.