The correct option is B Incorrect = there, Correct = their
Here, words like 'they', 'their fathers' indicate that there is more than one subject involved. So, option B) is incorrect. Option D) the does not fit correctly into the sentence. 'Theirs' is incorrect because it refers to something belonging to them. 'Best' is not a possession. So, option C) is also incorrect. Hence, the correct answer is option A) incorrect= there, correct= their.