The correct option is D do my brothers
Sentence B is supposed to reiterate the fact spoken in Sentence A. The speakers in both the sentences are different. Sentence B's speaker is giving a response to Sentence A's speaker by reiterating the fact spoken in Sentence A. So, Sentence B will have a verb emphasizing the fact already spoke in Sentence A. Hence, ‘do’ would be used after ‘so’ as an emphasizing verb. This is also because the Sentence A is in present tense and so the response of Sentence B would also be in the present tense only. Also, Sentence B's speaker is also mentioning this fact about his or her brothers and so ‘my brothers’ would come after ‘do.’ Hence Option C is the correct answer.