I. A, B, C, D, E and F are six members of a family. II. One couple has parents and their children in the family. III. A is the son of C and E is the daughter of A. IV. D is the daughter of F who is the mother of E. How many female members are there in the family ?

E is the daughter of A and F is the mother of E So, A is the father of E and hence the husband of F. Now. 

D is the daughter of F So. D and E are the daughters of A and F Also. A is the son of C. 

Now, only B remains Thus. B and C are the parents of A. 

Clearly, the females in the family are : either B or C, F, D and E.