Is it permissible for a person to marry his maternal cousin to conceal her pregnancy from his younger brother who is mentally incapacitated, and what is the ruling on the fetus in this case, and will the father incur wrath if the son divorces his maternal cousin to marry another?

Scholars have differed regarding the validity of marriage to a woman pregnant from adultery. The preponderant view is that it is valid, and the child is attributed to the owner of the bed if born six months or more after the marriage contract, and attributed to its mother if born in less than that time. Obedience to one's father is obligatory in matters that do not involve disobedience to Allah or what is contrary to custom and good. A father does not have the right to compel his son to marry someone he does not desire, and the son is not disobedient if he does not obey his father in this matter. Consequently, the elder brother is not bound by his father's condition that he return to the first wife and not divorce her. He may divorce her whenever he wishes without sin.