Women Who are Forbidden for Marriage, Dought & clear, - * Is my father a mahram to the wife of my half-brother through my mother?

<-:=:-> I have a half-brother through my mother who has got married,
praise be to Allah. Is my father a mahram to his wife or not?
-
Praise be to Allah.
He is not a mahram to her, because he (the questioner's half-brother)
is not his son; rather she is the wife of his wife's son. So your
half-brother through your mother is the son of your father's wife, who
is your mother. Therefore the wife of your half-brother through your
mother is a "stranger" (non-mahram) to him, and he is not a mahram to
her. If your brother divorced her, it would be permissible for your
father to marry her, because she is not the wife of his son, and she
is not the daughter of his wife, such that she would be his
stepdaughter. So he is not a mahram to her; rather she is the wife of
his wife's son, therefore she is a non-mahram to him.
And Allah knows best.
Fataawa Samaahat ash-Shaykh 'Abdullah ibn Humayd (may Allah have mercy
on him), p. 221

Women Who are Forbidden for Marriage, Dought & clear, - * 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

<-:=:-> Are the sister of my wife's grandmother and the sister of my
wife's grandfather mahrams to me?
-
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):"Forbidden to you (for marriage) are:… your wives'
mothers" [an-Nisa' 4:23]. So the mothers (and grandmothers) of wives
are mahrams, no matter how far the line of ascent reaches.
Please see also the answer to question no. 161869
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 fromFataawa 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."
And Allah knows best.