So to follow your logic, I can have multiple wives and every marriage is legal and binding. Polygamy in the US is officially recognized. Thank you for inventing this new law and right; the fundamentalist LDS churches will be glad for your assistance!
A marriage to an already married person is bigamy and is void by State statute. It never happened. Doesn't matter what you did to resolve it, it was void from the beginning.
Not quite. If one or both partners believed the marriage was legitimate, then it is Putative Marriage A real world example is one were a guy was shot down over Vietnam and declared to be KIA, whose wife then married his comrade in arms. They had several children together. Those children are considered legitimate, and there was no crime (bigamy is a crime). I forget how it was sorted out. Definitely an awkward situation.
But back to BHO, if Stanley Ann thought BHO Sr was legally able to marry her, and their is no indication that she did not so believe, then at least from her point of view, the marriage would fit the definition at the link above:
Three circumstances must concur to constitute this species of marriage. 1st. There must be a bona fides. One of the parties, at least, must have been ignorant of the impediment, not only at the time of the marriage, but must also have continued ignorant of it during his or her life, because, if he became aware of it, he was bound to separate himself from his wife. 2d. The marriage must be duly solemnized. 3d. The marriage must have been considered lawful in the estimation of the parties, or of that party who alleges the bona fides.A marriage in which these three circumstances concur, although null and void, will have the effect of entitling the wife, if she be in good faith, to enforce the rights of property, which would have been competent to her if the marriage had been valid, and of rendering the children of such marriage legitimate.