If it's your sister then your sister, if it's your brother's wife then you sister-in-law
Nephews are the sons of your brother or sister. Therefore nephews who are not brothers to each other are first cousins to each other.
Great nephew
He is their Uncle and they are nieces and nephews.
Second cousins.
Your brother-in-law's children are your nephews and nieces.
Your brother's children would be your nieces and nephews.
If she is not your mum then there is no relationship unless your father married her in that case she is your stepmother.
famous nephews include: R kelly Solja boi The Dream
your mum had sex with them all thats the relationship
Your sister's husband is your children's uncle. They are his nieces and nephews.
Your borther-in-law is your grandchildren's great uncle. They are his great nieces and great nephews.
ya mum!