The sister of the wife’s grandfather and the sister of her grandmother are mahrams

Are the sister of my wife’s grandmother and the sister of my wife’s grandfather mahrams to me?

The sister of the wife’s grandfather and the sister of her grandmother are mahrams to the husband just as her paternal aunt and maternal aunt are mahrams to him.

Praise be to Allah.

The wife’s grandmother – whether through her father or her mother – is a mahram to her husband on a permanent basis as soon as the marriage contract is done with her granddaughter, because she is included in the verse in which Allah, may He be exalted, says (interpretation of the meaning): “Prohibited to you [for marriage] are your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters, your [milk] mothers who nursed you, your sisters through nursing, your wives' mothers, and your step-daughters under your guardianship [born] of your wives unto whom you have gone in. But if you have not gone in unto them, there is no sin upon you. And [also prohibited are] the wives of your sons who are from your [own] loins, and that you take [in marriage] two sisters simultaneously, except for what has already occurred. Indeed, Allah is ever Forgiving and Merciful.” [an-Nisa’ 4:23].
So the mothers (and grandmothers) of wives are mahrams, no matter how far the line of ascent reaches.

The sister of the wife’s grandmother comes under the same ruling as her maternal aunt, so she is prohibitted for marriage to the husband on a temporary basis, so long as his wife is still married to him. But if his wife dies or he divorces her and her ‘iddah ends, it becomes permissible for him to marry her grandmother’s sister. Similarly, the sister of the wife’s grandfather is also prohibitted to the husband on a temporary basis, because she comes under the same ruling as her paternal aunt.

The scholars of the Standing Committee said:

"The grandfather is regarded as being the same as the father regardless of whether he is the grandfather on the father’s side or the mother’s side."
End quote from Fataawa al-Lajnah ad-Daa’imah (17/355).

Al-Bukhaari (5109) and Muslim (1408) narrated from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “One should not be married to a woman and her paternal aunt, or a woman and her maternal aunt, at the same time.”

See also the answer to question :
"Is it permissible for him to marry the daughter of his wife’s sister after she dies?"

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]

And Allah knows best.