one's younger brother and his wife
Refers to the couple consisting of one's younger brother and his spouse. Used when talking about family relationships.
I hear my younger brother and his wife are moving to a new house next month.
I received a souvenir from my younger brother and his wife.
Refers to one's younger sister and her husband; 弟夫婦 is specifically for a younger brother.
Compound of 弟 (younger brother) and 夫婦 (married couple).