Answer:
The correct answer is madre.
Step-by-step explanation:
My brother's mother is my mother, since if he is my brother we share the same parents.
There are many family members in Spanish.
You must analyze the link between them to determine which one is correct. Below I will write some of the most common family members in Spanish:
Madre, Padre, Hermano, Hermana, Tío, Tía, Sobrino, Sobrina, Abuelo, Abuela, Cuñado, Cuñada, Primo, Prima, Suegro, Suegra.