It all started when once I was with my GF having sex at her home. We rushed a bit and I didn't take all the precautions I always do. I didn't close the door completely. Well, while we were at it her dog opened the door (I'll skip what we were doing with him lol) and we didn't mind and kept going. Just because the dog turned his head over the door I did too and I saw her younger sister was there standing... Petrified... Standing motionless...
My GF is quite jealous, but idk how and why but I took the courage to ask her to come in and not stand there. My GF looked at me surprised and nervous, well, I was nervous too because we both just got caught mid sex. She slowly came to our bed step and saw us naked. My GF was dripping (she always gets very wet) and her sis noticed the wet spots in our bedsheets. I, again, took the courage to take her hand and put it over one wet spot and made her run her finger over it. Then I licked her wet finger. My GF was still very confused. I then took her hand and put it over her sister's wet thighs and slowly drew then over my GF's pussy.
I don't know how to explain, but we all had nervous but curious faces... I then began to kiss my GF on the neck (tbh mostly so their jealous attacks wouldn't kick in right in that moment) and I know her neck is a very sensitive spot. She started moaning and rubbing her legs against the sheets, against me and just a little again her sister's hand. I then went lower and started kissing her nipples (I know she can orgasm by that stimulation) and she closed her eyes, so I then grab her sister's hand and took her middle and ring fingers and pretty slowly rubbed my GF's pussy with them, then, again slowly inserted then inside my GF. She moves like a snake before orgasming. Her sister never saw something like that, she was worried, scared, she kept looking at me and I somehow made her understand it's alright. My GF is a squirter, that surprised her sister a lot!
That was their first time playing together. It was like a small introduction for all of us. I'll share what we did next after some acceptance from my GF about what we experienced that day that made her open to try more things with her younger sister.