Freud was quite a single-minded writer of fiction always carried away with his imagination, and an absolutely lousy scientist. How many people have been diagnosed absurdly and suffered immensely on the basis of Freud´s oversimplified concepts of the human psyche.
I can never take any reference to Freud seriously. Take the famous so-called Freudian slip, for example: In almost all of the cases it is just a simple language error that anyone would easily fall for. It is nothing to do with what the person really thinks deep inside.
I have never had any desire for sex with my mom and my sister, and neither did the both of them have such desires with me. Not in the least, not even in the faintest of hints. It was a loving family in the best and most innocent sense.
And I just don´t get it why the sheer mention of or question for long-haired relatives here gives rise to one-sided fantasies, assumptions, or accusations of incest.
I rather understand it as: Were or are there relatives around in your family that have inspired, started, caused, or nurtured your preference of long hair? If there were, it doesn´t automatically mean that a person with our preference actually wants or wanted to have sex with that relative, too.
And even if you leave the circle of your family - there are thousands of (very) long-haired women out there whose sight I enjoy, and with whom I still wouldn´t want to have sex, even though long hair triggers me the most.