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Your brother would call your husbands sister by her first name. Or, "my (sibling's) sister in law.
The relationship of the sibling of your sister-in-law or brother-in-law to you does not have a name in English. You could call them your brother- or sister-in-law if you want, or you can call them the brother or sister of your brother- or sister-in-law.
Nephew: your sibling's son (from your brother or sister); sibling: your brother or sister (from your parents). Because your brother or sister cannot also be your parents, and vice versa, your nephew cannot be your sibling. If one of your parents mates with one of your siblings, the resulting child would be a step-sister or step-brother, having only one parent in common with you.
Your niece.Your brother's daughter would be your niece and you'd be her uncle or aunt. Your sister's daughter would also be your niece. If your sibling had a son, he would be your nephew.
It is your sister's or brother's son, your adopted sister's or brother's son or your half sister's or brother's son. That would make you an aunt or uncle.
Your sister-in-law is either the sister of your spouse or the wife of your brother. In either case, she would call you her brother-in-law.
If they are biological brothers/sisters then they either have the same mother OR fatheror have both the same mother AND father.If they are brother and sister by law then they're brother-in-law or sister-in-law brother-in-law if that person is male and is the brother of the person your biological brother or sister marriedsister-in-law if that person is female and is the sister of the person your biological brother or sister marriedIf the biological brother has a romantic relationship with the biological sister then their relationship will be called incest.
Short answer: They would be your niece and nephew.Long answer:Your sister-in-law is either your sister-in-law because she is married to your brother (or, in same-sex marriages, your sister) or because you are married to her brother (or sister in same-sex marriages). If it is the former and she married your sibling, then her children would be your niece and nephew by blood--you share the same gene pool--happy swimming). Or, if it is the latter, and you married her sibling, then they are your niece and nephew by marriage and you do not share the same gene pool--unless there is another familial connection. Either way, you still have to buy them Christmas and birthday presents!
Your sister-in-law is either the wife of your brother or the sister of your spouse. Your brother-in-law is either the husband of your sister or the brother of your spouse. So your brother-in-law's wife is either your sister or is not related to you. Some people incorrectly refer to a brother-in-law's wife as a sister-in-law.
Your brother-in-law's sister is not related to you if your brother-in-law is the husband of your sister. If your brother-in-law is the brother of your spouse, your brother-in-law's sister could be your wife, but otherwise would be your sister-in-law.
Uncle or Auntie on your part depending if you're male/female. Their son is your Nephew (a daughter would be Niece). It makes no difference if the sibling involved is your brother or sister to this :)
If your sister-in-law is the sister of your spouse, her brother is the brother of your spouse and your brother-in-law. If you are a woman, and your sister-in-law is the sister of your husband, then her brother could also be your husband.If your sister-in-law is the wife of your brother, then her brother is not related to you.no relation