Is the grandfather's wife considered as a Mahram (unmarriageable relative)?
And likewise, is the grandmother's husband considered as a Mahram in regard to the girls?
It is permissible for a grandfather’s wife to be unveiled in front of her husband’s grandsons from another wife and their descendants, as they are Mahrams to her. The same applies to the girls, they are permitted to unveil in front of their grandmother’s husband, as they are considered as his stepdaughters and he is a Mahram to them. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.