We use a pair of commas in the middle of a sentence to set off words that are not essential to the meaning of the sentence. Use one comma before to indicate the beginning of the pause and one at the end to indicate the end of the pause. In the given sentence, the fact that Hari is the narrator's brother is not really essential to complete the meaning of the sentence. That is the reason why 'my brother' has been separated by a pair of commas. The sentence also promptly ends with a full stop and the proper nouns are correctly capitalized. Hence option B is the sentence with the correct punctuations.
Option A is incorrect because of the incorrect usage of the exclamation mark as we usually use it to indicate an exclamative clause or expression in informal writing. Also the proper noun 'Hari' is not capitalized correctly and the sentence is lacking a comma after the proper noun.
Option C is incorrect because 'Mumbai' is not capitalized and there should be a comma after 'my brother' to indicate a short pause.
Option D is incorrect as the word 'brother' is unnecessarily capitalized, the sentence is lacking a comma after 'my brother' and the sentence is ending with a colon which is generally used between two main clauses in cases where the second clause explains or follows from the first.