.
I used my three years younger sister, she was 12 (?), to show our younger brother (he was seven (?) years old) how girls look like. She cried, haha, because her "boyfriend" has stoped to be her boyfriend. And then also I was teasing her... Because our brother tried to touch her tits.
We've had fun, my siblings and I, but most of the time, not all of them found it funny...
But I dont find my sisters sexually attractive. So I dont have incest fantasies.