I told this story to my friend and he said I should post it her because people would like it so here I am.

So few month ago, I came to a party with my little sister(18 at that time) and on of my friend also came with his sister that I found very cute. During the party I flirted with his sister and noticed he did the same but didn't interrupted it since I was doing the same. I think you already see this coming, me and his sister went to a room and started making out. My friend opened the door and found us. He was with my sister and his sister said something like "come join us". It was a bit weird being next to my sister but didn't said anything. Both girls made us sit on a bed and unzip our pants and they started kissing each other. This made us instant hard and then the girls started sucking our dick. I saw that his sister was looking a lot to her brother dicks and even touched his balls for a few second.

We were fucking each other sister when suddenly while I was fucking his sister and mine was sucking my friend's dick, his sister decided to move and to go next to my sis. She then grabbed her brother's cock and started giving him a blowjob. We were so shocked but my friends didn't even asked her to stop. I was afraid that my sister would do the same but she didn't do anything at first. So while my friend was getting his cock sucked by his sister I was fucking her and my sister was getting eaten out by my friend. She was starting to look at me more and more but acted like if I haven't saw anything. She then came next to the pussy, looked at me in the eyes and said "would you fuck me bro ?" I was like no wtf. Then I told my friend to fuck my sister and we finished.

Till this day none of us ever talked about what happened but things aren't awkward.