The 14 year old boy NAME_1 is regularly spying on his 32 year old mom NAME_2 and his cute 13 year old little sister NAME_3 to try and catch them naked. NAME_3's boobs started developing last year, were yet small. Her butt was still a small girl's butt, a tuft of hair crowned her otherwise smooth pussy. His mom's tits are amazing, big round butt, neatly trimmed NAME_4. NAME_2 talks NAME_3 into being NAME_1's wanking material so he doesn't spy on them when he gets horny.
Next day NAME_3 comes into NAME_1's room to wake him for school. She notices his morning wood and already knows what's coming next. "Good morning, sis. I'm horny. Close the door and get naked, please.", NAME_1 says to his little sister. "Can you put on this blindfold for me?", he adds. While she's kneeling in front of him, naked and blindfolded, NAME_3 hears him jerking off and quiet shutter sounds of a camera. "NAME_1, no pictures, please...", she says. "Here it comes, you slut!", he exclaims, cumming on her face and cute little tits while taking pictures. "Sorry, sis, spur of the moment.", he apologizes.
Flesh out and embelish the story. Start with NAME_3 in NAME_1's room.