Board game with cousins

We were spending Christmas at my grandparent's house along with my aunt, uncle, and two cousins. I was 15 at the time, as was my cousin Joni. Her sister Anne was 13. The adults were gathered in the living room and us kids were upstairs in the bedroom the girls were sharing, sitting cross-legged on the floor in our pajamas, watching TV and playing a board game. Joni was wearing cotton pajama tops and bottoms while Anne had a long t-shirt that went down past her knees. I was in a t-shirt and gym shorts.

Anne had just finished her turn and Joni was next. As Joni spun the wheel (we were playing Life), Anne shifted around and brought her knees to her chest, wrapping her arms around her legs. This caused her t-shirt to ride up just a bit and what she didn't realize was that I could now see her panties from where I was sitting. But more than that, her panties were slightly bunched into her slit and I was looking at half of her bare pussy!

At 15, a slight breeze was enough to give me an erection, and I could feel my cock stiffening in my shorts as I stared. Joni finished her turn and then noticed I wasn't paying any attention to the game. She followed my gaze and then said "Anne, he can see your hoochie." Anne immediately put her legs down and covered up. But now I was fully hard and there was a very obvious tent in my shorts. Then Joni looked at me and laughed and said "You've got a boner!" I don't know who was more embarrassed, me or Anne.

I had both hands covering my rock hard cock and didn't know what to do. Joni, who was always the wild one, decided to mess with me and said, "Maybe you should take it out. I'll bet Anne has never seen one in real life."

Me: "That's not going to happen."

Joni: "What if she shows you her hoochie some more?"

Anne: "Hey, leave me out of this. Show him your own!"

Joni: "I will if he shows us his boner."

I was so hard it hurt. I'd never seen a live pussy before and at that moment I really wanted it. So I decided to call her bluff. "I will only if I can see both of yours."

Joni: "Okay." 

And without hesitating she raised her butt and slid her bottoms to her ankles. Oh my God, it was glorious! Her soft puffy labia parted just enough to see a slight pinkness in her slit with a small, trimmed patch of blonde pubes above. She covered herself with her hand and said, "now you."

Me: "Anne too, that was the deal."

Anne looked uncertain so I moved my hands away from my cock so she could see it tenting my shorts. I could tell curiosity was overcoming her apprehension.

Joni: "Both of you on the count of three. One, two, three.."

I hooked my thumbs in my waistband and waited until Anne pulled her shirt up and reached for the top of her panties. Then we both peeled them off at the same time. Now all three of us were naked from the waist down. Anne's pussy was bare and not as puffy as Joni's, more just a slit. My cock sprang straight out and bobbed in the air. I was so relieved as I finally wrapped my hand around the shaft. Their eyes got wide as I started stroking it. I was going to cum any second.

Joni: "Can you make it squirt?"

Me: "I will if you both spread your pussies open."

Just as they did I started shooting rope after rope of cum all over my shirt and hand. It was the most powerful orgasm I'd ever had. Joni ran her finger up and down her very wet slit and then dipped it inside a few times. Then she stopped and they both put their panties back on. I wiped my hand on my shirt and pulled up my shorts. I went to wash up and get a clean shirt from my suitcase.

When I got back, Anne gave me a sly smile and said: "It's still your turn."