The relationship between the father's wife whose marriage is not consummated and her stepsons
Signing a marriage contract between a father or a grandfather and a woman makes her a Mahram (unmarriageable relative) to all his children and grandchildren. She takes the same ruling as a stepmother, even if they do not consummate the marriage. This is according to Allah's saying: (Part No. 17; Page No. 352)
And marry not women whom your fathers married
Thus, it is permissible for her to reveal her face in front of her husband's sons and grandsons. As for the daughters of the woman whom your father married but did not consummate the marriage, they are considered non-Mahrams (not unmarriageable relatives) to him; it is impermissible for them to reveal their faces in front of him, as
Allah (Exalted be He) forbade a man to marry his stepdaughters, provided that the man has consummated his marriage with their mother. Allah (Exalted be He) says:
...your step daughters under your guardianship, born of your wives to whom you have gone in - but there is no sin on you if you have not gone in them (to marry their daughters)
Going into them means having intercourse with them. Thus, it is permissible for that man to marry one of these daughters. However, if he had consummated his marriage with their mother, they become his stepdaughters; it is forbidden for him to marry any one of them; and it is permissible for them to reveal their faces in front of him. This is according to the previously mentioned Ayah. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.