Family Structure Analysis

From the given statements, we can deduce the complete family tree. This is the same set of relationships as the previous puzzle.

• Grandparents (First Generation): E (male) is married to D (female).
• Parents (Second Generation): Their son, B (male), is married to C (female).
• Children (Third Generation): B and C are the parents of two children, A and F.

Determining the Genders

The clues allow us to determine the gender of every person except for A:

• E, B: Male
• D, C, F: Female (F is a "granddaughter")
• A: Gender is not specified. The clue "D is the grandmother of A" works whether A is male or female.

Evaluating the Statements

With this information, we can now test the truthfulness of each option:

A. A is brother of F

This statement can only be true if A is male. Since we do not know A's gender, we cannot confirm this.

B. A is sister of F

This statement can only be true if A is female. Since we do not know A's gender, we cannot confirm this either.

C. B has two daughters

We know F is B's daughter. For this statement to be true, A must also be a daughter (female). Again, this depends on A's unknown gender.

Conclusion

Since statements A, B, and C cannot be proven to be true based on the given information, the correct choice is that None of the statements are definitively true.