When my wife and I were younger, and just dating we used to set up role play scenarios on yahoo chat. This was back in the heyday of yahoo chat when it had user created rooms and way less monitoring.
We were both 19 at the time, but more often than not she would "play" 16. They way it usually went is I would get on cam and just chat with people that had similar interests as myself. Usually get on cam for them. The cover story was that I was home for the weekend from school. No one was home except my 16 year old sister, and she was busy doing whatever girls do. At some point, usually while I was masturbating, my wife would open the door behind and watch. I'd play like I didn't know what was going on until the guy/couple I was talking with mentioned she was there.
From there we would play it a few different ways. Sometimes I'd get really embarrassed and she would be the initiator. Sometimes I'd invite her over. In the end it usually ended up with her blowing me or me fucking her.
One of the more extreme scenarios we put on was I chatted up this older guy that had a thing for younger chicks. I gave him my wife's or..."sister's" ID and told him to chat her up and see what she was doing online. After a few times he "got her" to strip for him. I told him to set it up so that some weekend I would be home and he would get her to bate for him, I'd come in so I could see it. He did this, and as I came in the room and saw my wife played like she was shocked and wanted me to leave. She played that she was incredibly pissed at me for seeing. I ran up on her, threw her on the bed and "raped" her. When I was done I pulled out and shot on her face.
Afterward she just turned off her computer without saying anything and never talked to the guy again. I let it go for a week and signed on my account to chat with him. He was elated. Kept calling me his hero. I told him she loved it so much she was my fuck slave now, and let him watch us fuck one more time.
I confess, I miss those times. We looked close enough alike that no one really questioned it. And my wife, while not all that skinny, had smaller boobs, so no one questioned her age either. Now, we're old/fat/parents. OK, not really all that old, or all that fat. But it would be harder for people to believe us as siblings as opposed to a couple. Plus, my wife got out of that. I tried role playing it a while and she stopped me before I could. For her, it was more about the show, not the sexual idea of siblings. Which is fine. But now she won't even get on cam or show off anymore. Stupid marriage and kids.