As I understand it, the actual legality of their union is suspect. In reading a discussion of Barry's autobiography, it was stated that Barry didn't check out the factuality of a marriage because he didn't know what he'd find. (I didn't read the autobio, myself; so this may be erroneous.)
Barack Sr was also a polygamist. After leaving wife & child in Hawaii, he married (without benefit of divorce) an woman on the East Coast. When he returned to Africa, where he had left his main squeeze, he returned to & married her...again, without benefit of divorce.
He may have been married to her before he left Africa, but probably not.
He may also have married again in Africa, before he was killed in the car wreck.
Even assuming he wasn’t married to Obama’s mother, the second & third marriages, and no divorces, are not really in doubt.