(A) service performed by a child under the age of 18 in the employ of his father or mother;

(B) service not in the course of the employer’s trade or business, or domestic service in a private home of the employer, performed by an individual under the age of 21 in the employ of his father or mother, or performed by an individual in the employ of his spouse or son or daughter; except that the provisions of this subparagraph shall not be applicable to such domestic service performed by an individual in the employ of his son or daughter if— (i) the employer is a surviving spouse or a divorced individual and has not remarried, or has a spouse living in the home who has a mental or physical condition which results in such spouse’s being incapable of caring for a son, daughter, stepson, or stepdaughter (referred to in clause (ii)) for at least 4 continuous weeks in the calendar quarter in which the service is rendered, and (ii) a son, daughter, stepson, or stepdaughter of such employer is living in the home, and (iii) the son, daughter, stepson, or stepdaughter (referred to in clause (ii)) has not attained age 18 or has a mental or physical condition which requires the personal care and supervision of an adult for at least 4 continuous weeks in the calendar quarter in which the service is rendered;