X & Y Are Married

X & Y are married. They have a daughter who is 5 years old. They are living separately in fact. Y left the custody of her child to Z, her sister and went to live with S, a married man. S & Y wanted to get back the custody of Z. Will the action prosper?

A) Yes. They can because parental authority is inalienable.
B) Yes. They can because a child below the age of 7 cannot be separated from the mother.
C) No. They cannot because it would be impossible to have a moral development of Z under an immoral environment.
D) Yes. They can because in the line of preference of custody, Y has the right to have custody over her child.