When i was 16 and my sister was 13 we went on an ATV ride together. I modified the seat with a ridge down the center and got on behind her. We went to a very bumpy trail and I held her from behind as we rode. On a particularly large bump I grabbed her breast, pretending it was an accident. Her nipples were hard as rocks so I knew she was getting aroused from the seat. At one point when we were standing up to cross a rocky section i scooted forward before i sat back down and she came down right on top of my erect cock and gasped. We rode with her on my lap and i slid my hand up her shirt and fondled her breast and lightly bucked her to see how she would react. When she didn't freak out i readjusted myself and slid my hand under her ass covered by just bikini bottoms. I slowly slipped my finger into her slit and massaged her pussy as she lifted her ass slightly to give me better access. I took my chance and pulled my cock out of my shorts before pulling her back down, slowly guiding my dick inside her virgin pussy. The ATV came to a stop and she told me to stop, but offered no resistance. I drove all the way inside her and bucked aggressively as she quietly screamed. i picked her up off the seat and bent her over it sideways and covered her mouth with my hand and penetrated her once again. I fucked her until she came, then pulled my dick out and fingered her to lubricate my finger and guided into her ass hole. after getting two fingers in to the knuckle i pulled them out and put my dick slowly into her bum and she moaned as she slowly took my entire shaft inside her. As i began to pump her, suddenly another ATV came around the corner, but I was just about to climax. I pumped her a couple more times and exploded inside her bum right as my mom approached. She was in shock. With my cock still erect i walked over to my mom and grabbed her hand and guided it onto my dick. and told her she could be next. She was speechless so I pulled her off the four wheeler as she resisted slightly. i pulled her to the ground, yanked her shorts down and buried my face in her furry mound until she finally gave in. Once she settled i put my cock inside her and told her dad can never know. She cried silently as i pounded away. I came inside her pussy, stood up, and got on her ATV. As my mom and sister looked on in shock, I headed back to the house. This was a month ago and not a word has been spoken of it, but when my dad isnt home I make sure to walk around with my cock exposed. I don't know how this will end, but my two biggest fantasies came true and I got away with it. For now.