You would call your sister's daughter your niece.
The daughters of your sister are your nieces.
I call her Jane. There is no special name for a person in that relationship.
I believe it is your cousin-twice-removed. Definitely your cousin-once-removed's daughter.
To your sister's daughter you are an aunt (or uncle) and she is your niece. To your niece's daughter ( your sister's granddaughter) you are a great-aunt (or great-uncle) and she is your grand-niece.
Well my aunt is what I call my mother's brother's wife meaning we're not blood but that's normally how it works in most cases. Or at least with the first wife because my mother's other brother who remarried after his wife passed & I don't call her my aunt.
Your daughter's sister-in-law is either the sister of your daughter's husband or the wife of one of her brothers. If your daughter's sister-in-law is the wife of one of her brothers, then you would refer to her as your daughter-in-law since she is married to one of your sons. On the other hand the English language has no special term for the relationship between you and the sister of your daughter's husband. If you need something, you will have to call her your "daughter's sister-in-law" or your "son-in-law's sister." Perhaps your daughter has a half-brother who isn't your son, but whose wife is still your daughter's sister-in-law. In that case, this woman is not directly related to you. Not everyone likes to make such distinctions, and perhaps you could consider her to be an honorary daughter-in-law of yours, in the interests of friendship.
yes she can
Your brother's daughters are your nieces
Your brother's daughters are your nieces
There is no relationship at all.
the daughter's cousin
She is your third cousin.