Praise be to Allaah.
It is not permissible for a man to be married to two sisters at the same time or to a woman and her paternal or maternal aunt at the same time, because Allah says (interpretation of the meaning):
"Forbidden 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 foster mothers who gave you suck, your foster milk suckling sisters, your wives' mothers, your stepdaughters 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), - the wives of your sons who (spring) from your own loins, and two sisters in wedlock at the same time, except for what has already passed; verily, Allaah is Oft‑Forgiving, Most Merciful"
Shaykh 'Abd al-Rahmaan al-Sa'di (may Allah have mercy on him) said in his Tafseer (1/173): These verses refer to those who are haraam in marriage because of blood ties, those who are haraam because of breastfeeding, those who are haraam because of ties through marriage, those who are haraam because it is not permitted to be married to them and another woman at the same time, and women who are permissible in marriage.
With regard to those who are haraam because it is not permitted to be married to them and another woman at the same time, Allah mentions being married to two sisters at the same time and describes it as haraam. And the Prophet (blessings and peace of Allah be upon him) forbade being married to a woman and her paternal or maternal aunt at the same time. So if we take a pair of women who are related to one another, if we imagine that one of them is male and the other is female, if it would be haraam for them to get married, then it is haraam for them to be co-wives. That is because of what would result from that of severing ties between relatives. End quote.
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."
Ibn Qudaamah (may Allah have mercy on him) said, explaining the women who are forbidden in marriage: "married to a woman and her paternal aunt, or a woman and her maternal aunt, at the same time" - Ibn al-Mundhir said: The scholars are unanimously agreed on this matter and there is no difference of opinion concerning it, praise be to Allah, except that some of the innovators whose difference of opinion does not count, namely the Raafidis and Khawaarij, do not regard that as forbidden and they do not follow the Sunnah that is proven from the Messenger of Allah (blessings and peace of Allah be upon him), as it says in the hadeeth of Abu Hurayrah (quoted above).
The reason for the prohibition on being married to two sisters at the same time is that it would cause enmity among relatives and lead to severing the sacred ties of kinship, and this reason is also applicable in the case of marriage to a woman and her maternal or paternal aunt at the same time.
If they quote as evidence the general meaning of the words of Allah (interpretation of the meaning): "All others are lawful," [al-Nisa' 4:24], then the report we have narrated makes exceptions from that. End quote from al-Mughni, 7/89.
If you marry your girlfriend, you niece (daughter of your brother or sister) will continue to be your niece and will also be considered by most to be your new wife's niece. Your new wife will be her aunt, as you are already her uncle.
Your wife's niece is also your niece, and her daughter is your great niece. It is to be hoped that you do not have a relationship WITH her, merely TO her.
Your sister-in-law is either the wife of your brother or the sister of your wife.A niece of the sister of your wife may be your daughter. If not she could be your wife's niece too, as the daughter of one of your wife's other siblings. A niece of the sister of your wife could also be the daughter of your wife's sister's husband. In that case, she is not related to you.The niece of your brother's wife could also be yourdaughter or the daughter of another of your siblings, since your brother's wife is your daughter's aunt. If the niece of your brother's wide is the daughter of the wife's sibling, then she is not related to you.
Your wife's brother's daughter is her niece and your wife is her niece's aunt. Although you have no genetic relationship to your wife's niece, by convention your wife's niece is considered to be your niece and you are her uncle.
Your wife's nephew is also your nephew. His daughter is your (and your wife's) great niece.
I believe she is your 2nd niece in law.
Your sister's husband's sister's daughter might be called your brother-in-law's niece, although that is less specific than calling her your brother-in-law's sister's daughter. There is no term in the English language for a relationship between you and that person. You are not considered to be related.
your grand niece or nephew in-law (-Kasadie)
He could not find another wife.
"My wife's niece or nephew" Hi, in simple words, you could say it's your niece or nephew too; not necessary to be your wife's niece or nephew.
You and your wife are great uncle and great aunt to your wife's sister's granddaughter. The granddaughter is your great niece.