Correct:
This sentence stands for the simple future. We use the Spanish simple future to talk about what will or shall happen. It is also used to talk about the possibility of what someone may or might be doing in the present. In this way, podrá is the conjugation of the verb poder for the third person singular in the simple present. This sentence stands for the third person singular because mi hermano can be replaced by él (subject pronoun for the third person singular in masculine form meaning he). Lastly:
Mi hermano podrá ir a la escuela mañana means my brother will be able to go to school tomorrow.
