Entranced in carnal bliss, Mother and Father pay no attention to the creaking floorboards as your 16-year old brother goes to investigate the sounds, as he emerges past the banisters however, Mother and Father immediately revert into liquid form and take cover under the couch. Puzzled, your brother walks through the living room and heads down into the basement, unaware of the liquid trailing behind him.
"Mom? Dad? where are you guys?" your brother asks as he steps down into the basement, he reaches for the light switch, but of course its not working. He searches through the basement but it is clearly empty, as he turns around he sees a silhouette of a short, curvy figure approaching him.
"Mom? wha-." He is cut off by the figure pulling him in for a deep kiss, grabbing his hands and placing them on it's thick ass, Both moaning as they clutch each other and swap saliva.
Snapping out of it he pulls away from his mother, eyes adjusting to the dark he notices the lack of hair, and breasts, and....
"Mom? what happened to you? You have a cock?" He exclaims.
The figure stands silently, then grinning as a blue liquid pours down from the wall and builds up into a figure behind the young boy. Your brother quickly spins around but Father easily overpowers him, kissing his neck and removing his t-shirt as Mother removes his jeans and underwear.
"Dad, what are y-yy Mmmm!" your brother moans as his former parents continue to explore human sex further. Father sets him down on his knees, before laying down on his back and grabbing your brothers head, forcing his mouth over Father's large jelly cock. Mother too gets in on the action as he easily forces his slick cock into your brother's anus.
While both creatures enjoy fucking their new toy, their cells get to work, assimilating your little brother from both ends. Like Mother; your brother's gender begins to shift, his cock and balls retracting inside himself as his nipples puff up and breast tissue builds up behind them. Your brother slowly begins to actively enjoy the experience as his mind becomes foggy then abruptly is taken over by the hive, further changes to his body also occur, the short blonde hair on his head retracts into his scalp and the bone structure begins shifting, a more feminine face and wide hips form to match 'her' new dripping pussy and now D-cup breasts. Following suit her flesh turns to a new yellow color and to complete your brother's transformation her waist snaps inwards, turning your brother into a delightfully curvy female.
You insert your keys into the door, returning from the store as your parents and sibling continue to fuck like rabbits in the basement. You remember your bro and girlfriend were sleeping so you carefully open and close the door and silently creep up the stairs back into your room.
Meanwhile, Mother, Father and Brother continue their orgy, Mother, intrigued by Brother's new hole, pulls his dick out from her ass and begins fucking her pussy, which causes Brother to writhe and shudder in pure bliss as Father continues aggressively deepthroating her. after around 5 minutes the creatures finally push themselves over the edge and climax in a shared orgasm. Unlike humans however, their alien appetite cannot be quenched so easily. Removing his cock from Brother's mouth, Father communicates with the other two
'There is one more, upstairs.' As he points to the ceiling.