An idea came to him. If he could go inside of anyone he wanted, was that actually restricted to vore? He felt it'd be worth trying, and if it actually worked, this would be the best place to test it.
Jeff crawled onto the bed behind his sister, and pulls his pants and underwear down, dropping them to the side as he moved closer. Despite the camera facing the two, he lifted the back of his sister's skirt, staring down at her bare butt. "She didn't wear her diaper today," he thought to himself.
He reached forward, his arms going underneath his sister's shoulders as he lifted her up, getting a squeak as he placed her in his lap. "Jeff, what are you doing?" She asked, not wanting to take her focus away from the game. "Well, I've got nothing better to do, might as well watch."
That seemed to be enough, at least for now. He reached a hand down between her legs to adjust her position, before feeling his erect dick graze her exposed pussy. He pulled her closer, holding her in the air slightly, before pushing it in... He got a second squeak out of her, but...