What would it be if there was a child born from incest of two people being brother and sister? What does it say in the Bible about Satan wanting a child from incest?
Incest is having sexual relations with a close family member. It doesn't necessarily have to be between a brother and sister. Leviticus 18:6-18 gives a list of relationship which were forbidden to ancient Israel and Leviticus 20:11-12, 17-21 gives the punishments for those who violate these rules. But none of these mentions what happens to children born of such an incestuous relation. I suspect that this is because God views children as being innocent of the sins of their parents. For example, when Israel refused to go into the Promise Land, God condemned them to wander in the wilderness for 40 years. However, He said, "Moreover your little ones and your children, who you say will be victims, who today have no knowledge of good and evil, they shall go in there; to them I will give it, and they shall possess it" (Deuteronomy 1:39). God holds the people who commit sin as guilty, but not the innocent by-standers who suffers the consequences of another person's sins. "The soul who sins shall die. The son shall not bear the guilt of the father, nor the father bear the guilt of the son. The righteousness of the righteous shall be upon himself, and the wickedness of the wicked shall be upon himself" (Ezekiel 18:20).
There is nothing in the Bible regarding Satan wanting a child from incest.