Your sister-in-law is not related to your spouse unless she is your spouse's sister.
He would be your brother !... Unless, of course the sister-in-law had remarried after divorcing your brother - in which case, her new spouse would be no relation at all.
occured
If your brother-in-law is your spouse's brother, then his sister's daughter is your spouse's niece, and your niece, too. If your brother-in-law is your sister's husband, then his sister is not related to you, and neither is her daughter.
When your sister-in-law is the sister of your spouse, her sister is also your sister-in-law, unless she is your wife.When your sister-in-law is the wife of your brother, her sister is not related to you.
There are two ways you can have a sister-in-law.Your sister-in-law is the wife of your brother. In that case, her husband is related to you. He is your brother.Your sister-in-law is the sister of your spouse. In that case, her husband is your spouse's brother-in-law but is not related to you.
if your sims spouse has a brother or sister then they will be your sims brother or sister in law
There is no actual blood relationship. You would typically introduce her in that way, My son-in-laws's sister. Many refer to her as the sister-in-law.
If your sister-in-law is the sister of your spouse, her son is not related to your sister's son. If your sister-in-law is the wife of your brother, her son and your sister's son are first cousins.
Your sister-in-laws are your sisters by law after marriage. They are either your spouse's sisters, or the wives of your brothers. Their relatives are not related to you, although some of them will be related to your children.
Your spouse's sister is your sister-in-law and your spouse's brother is your brother-in-law. The English language has no term for a relationship between you and the wife of your brother-in-law or the husband of your sister-in-law. The best you can do in English is to use "my sister-in-law's husband" and similar phrases.
Your brother-in-law is your brother-in-law because he married your sister and his siblings are are only her in-laws not yours, so his sister is just your brother-in-law's sister. She's not related to you to you. Your brother-in-law can also be the brother of your spouse. In that case, his sister is the sister of your spouse, and your sister-in-law.
If your sister-in-law is the sister of your spouse, her brother is your brother-in-law (or your husband if you are a woman).If your sister-in-law is the wife of your brother, then her brother is not related to you.
In western (American) culture there is no accepted description of any relation between them. They are simply referred to as 'in laws' of their child's spouse.