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.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
Nephews and/or Nieces
if they are the children of your brother, they would be your nephews and nieces - if they were her children before she married your brother, then step-nephew and step-nieces
Uncle if you are male and aunt if you are female.
Second Cousin
Great-niece.
Your brother's daughters are your nieces
I can give you several sentences.My nieces are coming for a visit.Are those girls your nieces?Nieces are the daughters of your brother or sister.
Nephews and nieces
your 2nd niece...!
I have three nieces. One of my nieces has had her hair braided. My other two nieces are jealous of her. My niece's braided hair is a honey-golden brown. My nieces' mother is married to my oldest brother.