My experience would fit with your suspicions, for I had a long-standing incestuous relationship with my older sister that served more to bond an already healthy connection that has lasted all these years to now.
I’ve written of our early sexual awakening, at least with each other, of the halting and hesitant attraction we discovered for each other and how that slowly progressed. Some readers, looking for fantasy fulfillment perhaps, have registered a modicum of disappointment that (so far) haven’t done it yet. But that slow-as-molasses mutual seduction was as it really happened. While there was more to occur between us, I’ve not written more than the first ten chapters and this small novel. For your purposes, the experience, based on openness and honesty, served us well. We came to know ourselves, our sensuous and sexual selves well in our incestuous relationship. We remained close, at first physically as well as emotionally, and later, on different sides of the country, there continues to exist a strong tie of warmth and trust. To this day I fantasize about her.
I’ve not written about the fantasies I had about my mother. That remains in the shadows of my closet.