You are her niece or nephew (niece if female, nephew if male) and she is your aunt.
sister-in-law
You are his uncle, he is your nephew.
A reflective relation is one where the relation holding between A and B implies that the relation also holds between B and A 'sibling' is a reflective relation. A is B's sibling implies that B is A's sibling. In contrast, 'sister' is not reflective, A is B's sister does not imply that B is A's sister (for B might be male).
Hailie Jade Mathers doesnt have a bioloical sister but kim had a daughter from her previous marriage and eminem and kim had adopted their niece Lainie or Alaine so her cousin is her sister and a step sister
she would be your sister in law
There is none.
They were brother and sister.
Your sister and your wife are sisters-in-law to each other.
Real sister, half sister, or step sister
sister in law.
Your sister's sister is your sister.
The English language makes no distinction between an elder sister and a younger sister, or their children. Your sister's son is your nephew.