You are an aunt/uncle-in-law! Congratulations!! You really are; because you're an aunt/uncle to your niece you are now an aunt/niece by marriage to her husband.
You would be a first cousin by marriage, in other words, there is no direct relationship between you.
Second Cousin
Great-niece.
your 2nd niece...!
Nephews and nieces
They are your nieces and nephews.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
He is their Uncle and they are nieces and nephews.
The children of your husband's siblings are your nieces or nephews. Their children are your great-nieces or great-nephews.
They would be great nieces or great nephews.
They are your great nephews and/or great nieces. Alternately, some people say grand-nephews, grand-nieces.
It says what relation are your brothers nieces to you.... It could be your child or your niece also causes you can have two brothers and it may be the other ones kids. Or of course it could be your brother's new wife kid by another man making her no relation.