In the old testament the bible teaches us a good guidelines on what it is about marrying a close relative. During the days of Israelites in the bible gives a clear instruction on the boundaries to avoid such marriage.
Leviticus 18:6 says, “None of you shall approach any one of his close relatives to uncover nakedness: I am the Lord.”
These instructions given to the Israelites where not just a mere instructions but to preserve the love and care of a family. Marrying close relatives could lead to confusion in family roles and potential harm, both morally and physically. The Bible shows that God values order, respect, and dignity within the family, and these laws helped maintain those principles among His people.