To answer this question, we need to count the number of people in the family.
Given that Mr. and Mrs. Smith have six daughters, we know there are 6 daughters + 2 parents = 8 people in the family so far.
The question states that each daughter has one brother. Since we are counting the number of people, we need to consider the brother as well. Therefore, we need to add 1 to the count.
Hence, the total number of people in the family is 8 + 1 = 9.
Option A) 7 - This option is incorrect because it does not account for the brother.
Option B) 9 - This option is correct because it includes the brother and accounts for all family members.
Option C) 8 - This option is incorrect because it does not include the brother.
Option D) 10 - This option is incorrect because it overcounts the number of people in the family.
Therefore, the correct answer is B) 9.