The Ruling on Marrying the Daughters of the Father's Wife by Another Man
Question:
My father married another woman and she bore him a daughter then he divorced her and she married another man and bore him some and daughters. The question is: Is it permissible for me to marry one of the daughters from the other man? Advice me and may Allah reward you with goodness.
Answer:
There is no sin in that, as long as there are no ties through breast-feeding between you and her, nor any ties of kinship which would prohibit it. Her daughters are only forbidden to your father, because they are step-daughters for him, since he has had sexual intercourse with their mother. And Allah is the Granter of success.
Source:
Shaykh `Abdul-`Azeez Bin Baz
Fatawa Islamiyah Page no.226 Vol: 5