What is the ruling of Sharia on the marriage of a man to his brother’s wife, when his brother went missing and was presumed dead, then the first brother returned to find his wife married to his (other) brother and having had children with him?

If a woman marries after having a strong presumption of her husband's death and observing the waiting period (iddah) of death, and then her first husband reappears alive, there is no sin upon her or upon the one who married her. This marriage must be annulled, and the woman returns to her first husband after her waiting period from the second husband ends with the delivery of her child, according to the Almighty's saying: "And for those who are pregnant, their term is until they deliver their burdens." The first husband is prohibited from cohabiting with her until her waiting period ends, as a precaution for lineage, but he is not prohibited from entering upon her, being alone with her, or looking at her. As for the second husband, he is prohibited from all of that because he is a stranger to her, and the child is attributed to him due to the شبهة (semblance/doubt).