All characters engaged in sex are over 18.
*****
Some hours after their incestuous threesome, Robbie was dozing in the armchair, spent, still naked. He'd not managed another erection before he dozed off. His sisters on the other hand, had used the time well. Sarah was showing Kelly all sorts of things, guiding and coaching her about her own body. At one point, Sarah showed her how to find her G-spot and they both masturbated, watching each other, cumming just seconds apart with their eyes glued to each other's rapidly-frigging hands buried in folds of reddened female flesh.
They spent some time just cuddling, still naked, chatting about woman stuff like sisters do. Robbie began snoring lightly. Sarah grinned and beckoned Kelly to follow her. Putting cushions on the floor for their knees, she guided Kelly down beside her and she reached for Robbie's flaccid cock, now a shadow of its erect self. Sarah bent and put it in her mouth. Robbie didn't stir at first, even when Kelly took a turn. It was warm of course, salty with dried cum and pussy juice. Not delicious, not horrible either.
Inevitably, Robbie's dick stirred, rose slightly. He was moaning in his slumber. Sarah let Kelly enjoy the sensation of having a man's cock go hard in her mouth. For her part, Kelly was amazed that she was doing something now that just days ago she'd have thought dirty, nasty. She was sucking a cock. Maybe her objections had been overcome because it was her brother's cock she was sucking to full hardness. She loved him tenderly, so maybe that made it OK.
Robbie grunted, shot awake. It took a couple of seconds before he realised he had both of his naked sisters on their knees in front of him, sharing his now hard cock between their mouths. They giggled at his sleepy confusion and their own naughty boldness, then he simply opened his thighs, closed his eyes, and let it be.
He'd cum once already that night, but this erotic awakening had him ready to go very quickly. Kelly said to her sister, giggling across the shaft between their lips: "You reckon Robbie's got another root in him, Sair?"
"Reckon we should find out!"
Robbie opened his eyes and looked at them, smiling wickedly. Kelly went on between licking and nibbling her brothers cockmeat: "Let's see. He's fucked you, he's fucked me. He's licked my pussy... Wait! Has he licked yours yet?"
"Why no! I feel neglected and left out!" She was grinning wickedly, keeping her hazel eyes fixed on his as she bobbed her head down over his cockhead and took as much of his length in her mouth as she could.
Kelly continued the game: "Robert James Wilson! How could you..." She was jacking her brother now, Sarah licked the sides of his shaft. She went on: "That's so unfair. Why young man you fix that right now!"
Sarah stood beside him, as he lay back at an angle on the chair to get his mouth to the right height. Sarah put one leg over his chest, resting her foot on the seat of his chair. Robbie gazed lustily at the delight she now offered, just inches from his face. He smelled the fragrance of earthy sex, both dry and new juices there and on her thighs. He watched as his sister parted her pussy with two fingers, exposing her bright pink tunnel, her little hood, and the tiny bud of her clitoris.
He reached up and put two fingers in her. She gasped, threw her head back, and shuffled towards his face. He complied. Robbie tasted, then licked his sister's open pussy. His first contact made her tremble. She gyrated ever so slightly, rubbing her clit on his nose and lips as he lapped the juices flowing there.
Kelly was jacking him, watching the erotic show a foot away from her eyes. She saw wetness on Robbie's chin, a dribble of liquid turned to a droplet on her sister's thigh. Watching and learning, Kelly stroked the full length of her brother and occasionally bobbed her lips and mouth over the end. She took a closeup look at his balls for the first time, tickling them, amazed at their creased roughness and the weight of the orbs inside them. She knew not to squeeze hard there, treating them with tenderness.
