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.

Clearly, B and A are brothers. F is the brother of C. So, three brothers are A, B, F.