Many years ago, I took an advanced writing course through UCLA Online. (I was the only fantasy writer, but I don't recall having trouble with genre. I do recall being sort of bored with some of the other writers' plots. Come on, where are the sword fights and dragons? This needs more dragons.) The book I was working on at the time, Fey's Call, was an ensemble tale, but focused on reluctant heroine Tillian. Her first scene, she's about to meet up with her brother, who works for a group of rebels, and she's excited to see him again. This leads to his disappearance and then death, which sets her on a collision course with both his rebel allies and the authorities.
I was pretty floored when one of the other students said that the relationship sounded incestuous. It had never even crossed my mind that anyone would read it that way. I went back and studied the scenes, and maybe - maybe - could see it, but it was a stretch. I talked with someone outside the course about this, and they thought that perhaps it was reader bias - they were predisposed to such interpretations.
But I've always written about and been fascinated with family interactions, particularly siblings - despite, or perhaps because of, being an only child. I'm drawn to fictional families who are tightly knit and deeply loyal. What happens when a family member betrays you? If they commit a terrible deed? On the flip side of it, I love to write villains / antagonists who are nonetheless protective of their families and draw the line at anything that might hurt them. It's a dichotomy that intrigues me so much that I'll confess, when it comes to roleplaying games, I've just avoided making it a personal cliche.
You can have similar dynamics with friends or lovers, but this doesn't draw me as strongly. Shades of predestination, perhaps: you don't choose your family. Then there's also the societal aspects. Society has its own expectations of when a person should cut ties with a family member, and it doesn't always line up with personal experience. Then there's guilt by association. How do you deal with a family member dragging you down by nothing more than their chosen existence?
Or fame by association ... how do you step out of the shadow of a prominent sibling? One of the stories from the old Marion Zimmer Bradley's Fantasy Magazine that always stood out to me was about sorcerous siblings, one of whom believed she was created - that she only existed - to protect her sister, that she wasn't important on her own. That thought struck me to the core. It haunted me. I ended up writing a short story series (long before I was trying to get short stories published; it became more of a serial) about a girl who tries to pave her way out from under a famous sister ... and fails utterly.
And where in the world do you go from there?