You might want to call her sister-in-law, even though to the best of my knowledge there is no officially designated relationship for this situation. But I am certain that she will be very happy to be accepted with the above designation.
The husband of your sister-in-law is either your brother or the husband of your spouse's sister. In the later case, you would usually call him "my sister-in-law's husband."
co sister
Your brother would call your husbands sister by her first name. Or, "my (sibling's) sister in law.
You would call your husband's younger brother a brother-in-law.
brother in law
Sister-in-Law
You call your husband's senior brother simply a brother in-law. There is no difference whether he is a senior brother or a younger brother he remains your brother in-law.
If they were to get married then she would be your sister-in-law.
Yes
Your husband would call her Niam Tij, so if she married the older brother, you can just called her Niam Laus.
If person married to your brother is a woman? She is your Sister-in-Law.
I'd use her name. If the Brother in law is married to your sister, she would be your nephew's wife. And you are not related by blood.
Its would be your neice
In Scotland, you would call your brother "bruv" or "brother," similar to how you would in other English-speaking countries.