Dream Book: to See Incest in a Dream - Interpretation
Do not panic if you saw a dream about incest. Memories of this dream may bother you for a long time, but it is not necessarily related to sexual relations or deviations. Take a deep breath - and carefully analyze all the images and situation of the dream. The notion of incest involves a romantic or sexual attraction between relatives or directly sexual relationship between them. But most likely, it is an indication of less serious affection.
The object of our desire can be anima / animus (male and female archetypes), which manifests itself in the form of a brother / sister, but in reality is still a prototype of us ourselves. Then incest should be considered as a confirmation of our self-esteem or veneration of some quality, which we are endowed.
Another possible option is summarizing of the old relations in the light of new romantic attachments. So many children sometimes have a desire to marry the parent of the opposite sex. This is a natural manifestation the Oedipus and Electra complex described by Freud.
It is important to evaluate your feelings about this dream on awakening. If you are overwhelmed with the same feeling that after the violation of the sexual taboo in a dream, and those feelings come back from time to time, you may need professional intervention.
(Loff's Dream Book)