The correct answer is: D. No error
The sentence is grammatically correct. The use of “between my brother and myself” is correct, as it is a compound subject. The use of “and concerns nobody else” is also correct, as it is a prepositional phrase that modifies the verb “concerns.”
The sentence could be rephrased as follows:
Please try to understand that the dispute on this issue is between my brother and me, and concerns nobody else.
However, the original sentence is grammatically correct.