Mom's big butt

 "How's it feel to have mom's big butt?" Sarah teased her brother as she stroked one of his fat cheeks. "Stop," Ben said. "Mom and dad will be home soon. They'll kill us if they see us like this." 

But he didn't back away from the hand on his ass, and he let Sarah's other hand rest on his breast. 

"What's the big deal?" Sarah replied, "We're the adults now." 

Sarah's body was so horny, and her new cock -- her dad's cock -- was right there, dangling between her legs, calling out for attention. She'd walked in on her brother while he was in the shower and he protested, though not very much. Her dad's cock slowly rose to attention as she ran her hands along her mom's body. She never really appreciated the delicate female form until she saw it from behind male eyes. 

The whole family had been on vacation and discovered a magic board game that had swapped all their bodies, leaving the two siblings inside the bodies of their parents. 

Ben stayed still, trembling as Sarah stroked him. He slowly reached down and wrapped his fingers around her warm cock. She pulsed in his hand, growing larger and harder, her own explorations growing more urgent as she squeezed his fat butt and ran her hands between his legs. God, the feel of her mom's coarse pubic hair against her fingertips and the silky feel of her pussy as she slipped inside sent a fierce urgency through her. Soon she had her brother over the sink, plunging into his slick warm pussy from behind as he moaned. Only when she came, filling him with her hot cum, was the urgency sated.