Unexpected sex frenzy at family gathering with the in-laws

Me and my girlfriend were 27 at that time. We are together for few years and I know her family quite well. Her sister is 3 years younger, and I found her quite hot even if she doesn't try to much. She is a short brunette with wide hips and nice C-cup breasts. The sexiest thing about her is that she dress really light and short so you often get a glimpse of tits or ass. The mother is in her 50's and she was really hot when she was young, like a nice ass in those trendy 80s Levis jeans and above all large E-cup breasts, hardly unnoticed.

So we're all together, my girlfriend, her sister and boyfriend, her parents and me. We're having a nice dinner, we have a good time and drink a couple a wine bottles. We had a long road so around midnight, everyone is kinda tired and goes to bed upstairs. The house is small so the parents are in one bedroom, and the children in the other.

As everyone is upstairs, my girlfriend lingers in the kitchen and asks for a hug. By the way she kisses me I quickly understand that there will be more to this hug. She lowers her hand down to my crotch to feel the bulge of my beginning boner and kisses me more as she seems quite pleased with what she felt. "I didn't want to embarrass my sister" she said. She quickly unbuttoned my pants and get on her knees, looking up at me with a smile, as if she was asking wether or not I wanted this. I didn't plan it, but I wasn't gonna refuse this opportunity of getting my dick sucked by my very horny girlfriend.

A couple minutes later I'm already very hard, at least hard enough for her because she stands up and moves back to sit on the table, pulling up her dress and revealing her underwear. She looks at me and begins to touch her pussy, putting one finger deep inside so I could feel how wet and ready she is. She smiles at me and grabs my shirt to get me closer, and I know the only thing I have to do is to put my dick inside as quick as possible. She moans with pleasure when it gets in and lifts her legs to put it around my waist. After a few minutes, she seems to get bored with this position and wants to do something as slutty as she felt when she initiated this earlier. So she turns back, leaned on the table to have her ass in good position, then turns her head and says "Fuck me on this table". After this it went quite wild, my cock went back and forth in her pussy with strength, every time trying to hit it deeper and harder, and when I slapped her ass she was so excited and so embarrassed at the same time because even if we tried to be quiet, it was less and less sure we were indeed. She covered her mouth to mute her moaning and arches her back even more, fucking back with her ass to show how hard she wanted to be fucked. "Oh fuck, I'm cumming, don't stop !" I felt her body quiver with pleasure as she came. I was so turned on by this that I came inside her a few seconds later, filling her pussy with what I believe was one of my most powerful ejaculation.

We were short of breath, she went to the bathroom as I pulled up my boxers. Few seconds after this, I see the kitchen door opening, and thinking it was my girlfriend I act naturally. It was my sister in law, who went down to get some water. She stops when she saw me and looks quickly everywhere to understand the situation. Here I was, without pants, with only a shirt and boxers hardly hiding anything I've done a few minutes earlier, with a clear bulge of my remaining boner and a wet spot at the tip of my cock. In front of me, my sister in law wears only an oversize white T shirt underneath which you could see her nipples poking through, lenghty enough to cover her butt as long as she doesn't move. "I'm thirsty" she says. "Yeah, me too". She goes to the sink without really looking at me, but I know she saw my bulge, and I leave the kitchen wishing her good night. Before leaving, I looked at her as she drank, and saw her ass revealed by her thong as the shirt was lifted up by her arm.

I went up to join my girlfriend in our bed, and hear some noise in her parents bedroom. They always have the TV on, but this time it feels different. I slow down to listen, and hear my mother in law moaning as she was clearly getting fucked. I could even hear the wet sound of her pussy getting slammed. Her moans were incredibly arousing because I wasn't expecting it, and at the same time I couldn't help but picturing her and her large tits bouncing. After what happened downstairs, I was so excited again that my cock was hard as if I didn't just fuck earlier. I would have stayed and maybe jerked off but I heard my sister in law in the stairs. When she joined her boyfriend in bed, we were all pretending to be asleep, but neither of us were because the noise in the other room was quite distracting. I heard my SIL whispering something to her boyfriend, and the noise of sheets moving. My hard dick was pressing against my girlfriend butt as soon as I went under the sheets, and I kow she wasn't sleeping because evertime she moved, it was to get her ass closer to my dick. She just enjoyed it but I don't think she wanted to go further.

It went quiet, until I heard a strange wet sound. My SIL boyfriend wasn't sleeping, and as I listened closer, he breathes heavily. After a while I was 100% sure : she was giving him a blowjob under the sheets. It turned me on even more, especially because I wanted to believe that it was the view of my boner that made my SIL horny. I began to move my dick against my girlfriend, and she moved back slightly to feel it closer against her asshole. The suction sounds went louder, as if she cared less and less to be heard, or simply because she was so turned on. I thought maybe she wanted me to hear this and imagine it was my dick she sucked. Her boyfriend let go a deep sigh, and the room went quiet except for the sheets when my SIL went up to lie on the bed. My girlfriend moved her hand on my cock and gently caress the head with her thumb. After a few minutes of doing this, she felt a wet spot left by the precum on the fabric, and moved her thumb faster against the frenulum. She was doing it very quietly but I breathed heavily, because I kinda want my SIL to hear me, like a call and response between us. I wanted her to know that I would have wanted to fuck her and that she made me horny when I heard her gaving a blowjob to her boyfriend. I came in my boxers less than a minute after hoping my SIL knew I was thinking about her, and we all fell asleep.

I had nice dreams, and since then I often fantasize about fucking her sister and mother, even if it'll never happen. But I wouldn't lie, I sometimes catch a glimpse of tits or ass when I can.