Yes, Quinn teaches by example

Quinn sides down my body next to Robin and watches her trying again and again. Her hands reach for Robin's throat and touch behind the jaw. "See honey, you're just not relaxing the muscles to let it in. Let me show you." And with that, Robin slides off the couch and Quinn takes her place between your legs. Quinn looks up at you and you can see how bad she has wanted this. She slides down until I hit the back of her throat, makes a show of looking towards Robin to prove her point, and then relaxes her throat and proceeds to sink until her nose is pressed up against me. She's fucking amazing.

You grab Quinn's head and push it down a few times, feeling your cock sliding easily in and out of her tight throat, hearing the sounds of you hitting deeper. For a moment you almost forgot about your sister girlfriend. You pull Robin to you now, grabbing her tits and pushing them together before you start devouring them. Robin moans in response. You let Quinn up and she gasps for air. Her makeup is running down her eyes from the tears but she looks hungry for more. You push her back down and use her mouth a few more times until you cum hard in her mouth. "Don't swallow," you order. You turn Robin to face Quinn. She hesitates but then lunges forward to kiss Quinn and share your cum from her mouth.

When you ask if she thinks she learned how to do it herself, she nods enthusiastically and gets back between your legs. Your cock twitches and begins to harden again. Quinn sheds her shorts, now revealing her nearly trimmed pussy. She offers her breasts to you again, this time playing with herself as she watches Robin trying. This time Robin still struggles but successfully gets all the way down. You moan loud, making sure to show my appreciation for all the effort she's put in to my pleasure. Quinn seems excited as well and appears to be getting close. You pull Robin up and see the big smile on her face. She's about to drive back down but you stop her. "We're going to have plenty of time for that later, baby. I have something special I think should mark the occasion.

You direct the women over to the bed. At first they lay on their backs side by side looking up at you. But you direct them to move. You put Quinn on her hands and knees over Robin. They start making out and you get between their legs and pull your sister's ass up to reach you as you slide your cock into her soaked pussy. You hear her moaning into Quinn's mouth. You fuck her hard and deep, knowing that everything is going to push her to cum soon. Quickly you hear moans turn to screams and feel her pussy clamp down on your cock. You let her body fall back down to the bed. The kiss broken, Quinn stops and thinks the fun is over until you grab her ass and push your cock up against her slit.

She moans, pushing back and trying to **** your cock inside her. Robin absent mindedly fumbles her hands on Quinn's body, the big tits hanging in front of her mouth until she can stick her tongue out to lick. You grab her hair and pull back, whispering "careful what you wish for," before you bottom out in her with one easy thrust. Her sexy round ass looks and feels so good as you bounce against it.

"FUUUUUUCK!" she screams on your cock as she adjusts. Still holding her hair you start pounding her needy pussy harder and faster and she responds. "Yes yes yes... Use my pussy, I want to be your dirty little slut, ohmygodohmygodohmygodohmyGOOOODDDDDD" she screams as she cums hard on your cock.

You're getting closer too and you realize in a moment if clarity you have no idea about the birth control situation. You pull your cock out and shoot your load all over Robin's clit and insert thighs. Quinn hasn't recovered yet, but you still whisper in her ear that you want her to clean your cum off your sister girlfriend and that she'll get a reward if she makes Robin cum again in the process. Quinn quickly attacks Robin with her tongue, both for the cum and the promise of a reward. Soon Robin is both clean and cums again. When that is done, they both turn their attention to cleaning your cock with their mouths. You promise Quinn you'll give her that well deserved award later on.

In the meantime, you guys need to figure out how to get inside without getting caught. Quinn shows the most obscure route into the cellar then popping up into your room with barely any time in busy halls inside. You invite Quinn to shower with the two of you, as you can't just make her fend for herself walking around after just being fucked and deep throated. The three of you clean each other off. Quinn can't stop cleaning your cock and staring at it. She's clearly ready for whatever reward you can imagine as long as it involves that cock back inside her.