D is father of A and grandfather of F.
So, A is father of F.
Thus, D and A are the two fathers.
C is the sister of F.
So, C is the daughter of A.
Since there is only one mother, it is evident that E is the wife of A and hence the mother of C and C and F.
So, B is brother of A.
There are three brothers.
So, F is the brother of C.
Hence, B and A are brothers.
F is the brother of C.
So, three brothers are A, B, F.