The following individuals may adopt:
(1) A husband and wife together although one (1) or both are minors;
(2) An unmarried adult;
(3) The unmarried father or mother of the individual to be adopted;
(4) A married individual without the other spouse joining as a petitioner, if the individual to be adopted is not his or her spouse; and if: The other spouse is a parent of the individual to be adopted and consents to the adoption;
(5) The petitioner and the other spouse are legally separated; or
(6) The failure of the other spouse to join in the petition or to consent to the adoption is excused by the court by reason of prolonged unexplained absence, unavailability, incapacity, or circumstances constituting an unreasonable withholding of consent.