I've been enjoying this site for about a year and thought you might like to hear of my experiance a couple of years ago.
At the time I was 15 and my two sisters were 17 and 13, we had been sunbathing in the back garden and my sisters were sitting on deck chairs while I lay on a mat, our parents were doing work in the garden.
After laying on my back for some time I rolled over onto my front when Kirsty  asked me if I was getting burned. I looked up to answer her and found that I could see up her skirt and could see her pink panties. I said no, that I was getting my back tanned. She looked about and our parents were out of earshot. She said to Meg  that I was looking up her skirt, which I of course denied. They just laughed and said sure.
Later on our parents went out for a couple of hours and told Kirsty to look after us, she smiled and said I will. A short time later I was up in my room when I heard Kirsty call me to come down. I went downstairs and as I entered the living room they grabbed me and pulled me onto the floor.
I only had on my shorts with briefs underneath because of the heat. They tied my wrists to the legs of the table and said it was fun time. Kirsty asked me if I had been looking up her skirt and I said no, wrong answer she said and told Meg to take my shorts off. Meg gripped the waist band and slowly pulled my shorts down revealing my small white briefs and took them right off .
Kirsty asked me again and I said yes, right answer so for that we will give you something to look at. They then both took off their tops and skirts and were now standing in their underwear, Kirsty in pink bra and panties and Meg in white. I could feel my prick start to stiffen and they noticed. Kirsty knelt beside me and started rubbing me through my briefs and told Meg to have a feel, which she did.
'Would you like to see us naked?' Kirsty asked. I could only nod yes, so off came bras and panties and my two sisters stood naked in front of me, Kirsty has quite big breasts and a lovely bush of brown hair, Meg's breasts were nearly as big but her bush was more blonde. Now your turn Kirsty said and took my briefs off, my prick sprang up to its full size, 6' uncut, and they both started stroking it and playing with my balls.
After about five minutes Kirsty then gripped my prick in her fist and started wanking me off. Another few minutes and I sent a stream of cum shooting out over her hand and my stomach. Meg got us some kitchen towel and cleaned me as Kirsty cleaned herself. They got dressed and finally loosened the ropes and I got dressed. Kirsty later asked me if I had enjoyed it, I said yes. She also asked me if I would look up her skirt again and I said no (I lied , I'd look if I got the chance). She looked disappointed then said sure.
I never got the chance to touch them, although later times I did. When our parents came in they asked if everything was ok and Kirsty said everything went perfect, and gave me a smile.