This was told to me first hand, so forgive me if the gender point of view does not come out right.
Ours was a blended family with me being adopted and my three years older brother born of both parents. They were strict enough that they wanted to know where we were at all times, even in the house. But kids' curiosity can beat any parental rules. Often he would sneak into my bed because we liked to talk before drifting off. He always got up and went back to his bed before our parents woke up. When he was sleeping, I discovered his penis and was fascinated about how it would stiffen up to my touch, even when he was asleep. I honestly couldn't tell if he was awake and never had the nerve to ask him about it later.
One night he was facing away from me, thinking I was in dreamland but I could feel the bed shake. So I reached around and grabbed his cock, my smaller thumb and forefinger encircling the head just above his bigger fist tightly grasping his shaft. I quickly learned how to match his rythym, but just as his body was stiffening up-I had enough of my own orgasms by then to know what coming was, he pushed my hand away and quietly groaned, then did not say a word. After this he would let me get him started but still never let me finish him off. This only happened a few times because we got scared one night when mom got up early to take a pee, so our shared bed experience ended.
Eight years later my life had taken many twists and turns and I was now a stripper living 100 miles from my home town. One day I had a bearded young man for a private customer who got my top caliber of 'no touching' dance back stage. I suspected who he was, and knew for certain when he came back two days later. This time he got the full lap dance experience. My bare bottom ground agains his pants covered cock as he sucked first one then the other nipple as my breasts brushed against his thick beard. I was turned on myself, as he was getting a dry humping rythym that no man could resist. He groaned, got up and quickly left. Maybe he was afraid I was in on secret. But believe me, that secrecy had made it all the hotter for me too as I felt for the first time my brother's hot come on my naked skin.