You call them your nieces, or by their names.
You would refer to them as your nieces, thought they are formally your wife's nieces. And they would normally call you uncle.
You can refer to your sister's children as your nieces and nephews. If your sister has daughters, they are your nieces, and if she has sons, they are your nephews. Collectively, you can call them your nieces and nephews or simply refer to them as your sister's kids.
Some would call your nephew's children your grand nephews and grand nieces, others would call then your great nephews and great nieces.
Second Cousin
Nieces.
If it is a boy then it is your nephew. If it is a girl then it is your niece.
Your husband's sister's kids are referred to as your nieces and nephews by marriage. More specifically, you can call them your "nieces" if they are girls and "nephews" if they are boys.
Your brother's daughters are your nieces
Your brother's daughters are your nieces
The children of your husband's siblings are your nieces or nephews. Their children are your great-nieces or great-nephews.
yes
Mother in-law