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.
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 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
If you have two nieces who are not sisters but are each the daughters of your siblings, the two nieces are first cousins. If they each have a daughter, those daughters are second cousins to each other.
Second cousins.