It’s a deal

"Just slide right in there," Marcus's stepmom said, grabbing his cock and aiming it at her daughter's pussy.
Marcus's stepsister was stretched out on the couch in front of him, legs wide to reveal the puffy pink lips of her pussy, her hands squeezing her taut tits as she blinked slowly up at Marcus.
"Fuck me, big bro," she moaned.
Marcus's cock throbbed beneath his stepmom's fingers. She giggled and guided him in against his stepsister's warm pussy, his cockhead meeting resistance before suddenly slipping in. Marcus moaned, his body trembling as his stepsister's canal clutched his dick. Fuck, she was so warm and wet and tight, and he thrust in deep. 
His stepmom knelt beside him, one hand caressing his stepsister's tits as she brought her face between his stepsister's legs. Her little tongue flicked out, licking Marcus's cock whenever it slipped out of his stepsister's pussy, tasting them both before moving closer and licking his stepsister's clit.
Marcus's stepmom and stepsister had been acting strangely ever since coming back from vacation. When Marcus discovered that bodyhoppers had taken over their bodies and confronted them, they made a deal to buy his silence by fucking him every now and then.
It was now. And his stepsister moaned once again beneath him. He felt her quiver, a small orgasm pulsing through her. He held on only a little bit longer before finally releasing, thrusting in deep and filling her little cunt with his cum. When he withdrew, his stepmom buried her face between his stepsister's legs and licked his jizz up, coming up grinning, her chin slick with their mingled juices.
"Can't wait until next time," she laughed.