"Is there a law against stepsibling marriages?

If you wanted to marry your stepbrother or stepsister, there is nothing in U.S. law that says you cannot do it. There is no U.S. law that makes it illegal for stepsiblings to become lawful husbands and wives.

Even though you may be related through your parents' marriage, you are not related by blood, therefore, you are not subject to consanguinity laws, which make it illegal for close blood relatives to get married. Consanguinity laws make it a crime for the following relatives to get married:

• Biological brothers and sisters,
• Half-siblings,
• Aunts and nephews,
• Uncles and nieces, and
• Many states say it's illegal for first cousins to marry, however, all states say that second cousins are allowed to get married to each other.

Since stepsiblings are not blood relatives, they are legally free to marry each other. There are no state laws that prohibit marriage between stepsiblings since they are not at risk of having children with genetic defects due to being close blood relatives.

If you have further questions about your state's marriage laws, please contact a family law attorney!"

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- http://www.findafamilyattorney.com/Featured-News/2016/Is-it-Illegal-for-Step-Siblings-to-Marry-.aspx#:~:text=Since%20stepsiblings%20are%20not%20blood,to%20being%20close%20blood%20relatives.