Resist the temptation, but don't stop them.

You gently shift yourself from underneath Katie and nudge her towards Kelly. She's perfectly happy to oblige, pressing her petite body against Kelly's, the girls' hands pulling each other close aggressively. You hear Katie's breath inter-mixed with quiet moaning, while Kelly squeezes Katie's firm butt, then slides her hands around Katie's waist to unbutton her jeans. Katie breaks their kiss momentarily to quickly remove her T-shirt and deftly unstrap and toss aside her bra.

You find your eyes transfixed on Katie's perky tits, seeing that they're even more perfectly shaped than you'd imagined in your many, many masturbation fantasies.

Kelly seems to appreciate them just as much as you do, immediately leaning upward and kissing Katie's soft nipple, breathing "oh god" quietly as she finally loosens the last button on Katie's jeans. Katie looks down at Kelly, then grabs her hair roughly, pushing her head back and plunging her tongue into Kelly's mouth as she slides out of her jeans, her black panties sliding down with them. You see your naked cousin straddling your gorgeous step-sister, and once again contemplate your situation.

As you sit on the couch just next to them pondering, Katie yanks Kelly's shirt off, revealing a pink silk bra.