Except for afew ancient kingdoms who preferred keeping royal blood "pure" by marrying within families(sometimes even among step siblings), Incest was strictly forbidden by most African tribes.

Spiritually, incest attracts powerful demons...

This reminds me of the common stories I come across with defiled children being associated with families known for practicing witchcraft...

This not to disparage victims ... Moreso to help them understand the intentions of their attackers ... The evil have their day in waiting...

From the Kolbrin;
The book of gleanings,
Chapter 11

This reminds me of a sad story of defilement in which two sisters were defiled by the same man. It would have gone unnoticed if it they were not siblings. You see, they were both taken to a witch doctor by their guardian grand parents. I have come to learn that there is a special kind of witchcraft medicine which allegedly has to be applied in their womb hence their defilement

So the reason, I was told, why the act was reported as a defilement, is that when sisters sleep with one man, they should never be near each other when one falls I'll, or it will lead to the death of the sick one. I don't know what that means for men who marry sisters or sisters who steal each other's husband's ...

This is all because of the kinds foul of spirits that surround incest ...

So stay away from your relatives' spouses ... For your own sake.