As has been elucidated in various articles found with the Serpent Seed category: the Bible does speak the seed of the serpent and the seed of the woman. Yet, it does not, in any way, relate seed of the serpent to Cain being the result of Eve having sex with Satan.
In fact, since the serpent seed of Satan theory is not biblical, promulgators, such as those listed below, have different ideas as to who the seedlines / bloodlines are.