Older Sister Grinding

When I was younger my sister and her friend from school were hanging out in her room. They were about 2 or 3 years older than me and never really paid attention to me when they had their get togethers. This time she came and got me from watching tv and said she wanted some help. So I go with her to her room and her friend is there just grinning at me so I ask what they wanted? So my sister explains that they are going to a house party and her friend has a guy she likes and wanted to practice dancing.
So being the nob that I was I thought they meant like doing the running man or some shit lol. But they put on some club tunes and my sister puts me to stand against a wall and her friend backs her ass up on me and starts grinding. My dick gets hard immediately and the friend starts grinding harder. My sister ask is he hard and she laughs and says yes it's like a broom stick in my buttcrack and they both laugh. So Unbelievably my sister says lemme see and her friend moves and she backs up on my erection. So now my sister is grinding on me while her friend watches and they are critiquing each other and I'm losing it.
I'm pumping my hips driving my erection in between my older sisters asscheeks getting close to cumming and she moves of and says don't get too excited I'm still ur sister and laughs. So her friend says he was a good boy today let's let him finish. My sister laughs and says well you go ahead I can't. And her friend backs up on me again and I hump her ass to the beat with my sister in the room til I blow my load against her her ass. As I'm cumming the friend pushes back hard and squeezed every drop out with her butt. After my sister tells her well. all you have to do is dance like that at the party and the guy ( I can't even remember what name they said) is yours and then they put me out laughing.