Is The Husband’s Grandfather a Mahram to the Wife?
Question

I am trying to apply the teachings of our religion, such as prayer and fasting, and adhering to Hijab with non-Mahrams, but I cover my face and hands, and what ordinarily appears to the Mahram, in front of my husband’s grandfather. Are grandfathers Mahrams?
Praise be to Allah.Shaykh `Abd Al-`Aziz ibn Baz (may Allah have mercy on him) said:
May Allah reward you with good for your concern about religion and your keenness to adhere to that which Allah has made obligatory upon you.
With regard to your question about the husband’s grandfather, there is no doubt that he is a Mahram. The husband’s grandfather, whether he is the father of his father or the father of his mother, is a Mahram.
So there is no blame on you for uncovering your face and hands and so on in front of him, and there is nothing wrong with that. He is like all other Mahrams such as your brother, uncles and so on. (End quote)
To learn more, review these responses:
Who Is a Woman’s Mahram
Ruling on marrying the grandfather’s stepdaughter
The grandfather’s wife is a Mahram
His grandfather’s daughter is also his paternal uncle’s wife
And Allah knows best.