Bible fag here: Cain was human and born of Adam and Eve, same as his brother, Abel. The idea that the serpent and Eve had a sexual thing going is false.
Genesis 4: 1 "Adam lay with his wife Eve and she became pregnant and gave birth to Cain."
It doesn't get much more clear than that.
Gen 4:2 "Later she gave birth to his brother, Abel"
Nope