Probably your niece-in-law.
Your sister is great aunt to your daughter's child. The child is your sisters great nephew (if a boy) or great niece (if a girl).
The wife of your first cousin is not related to you.
Your daughter and your sister's child are first cousins. Your daughter and your sister's grandchild are first cousins, once removed.
You are not related as you do not share a common ancestor.
Yes you can marry her. She has no blood relation to you. She is just the niece of your brother's wife from her side. It is no different than if two cousins married two women who were sisters.
None of the Cimorelli sisters have a child.
No Justin Moore is an only child and Kip has 2 older brothers and 3 younger sisters.
cousin
brother-in-law
Great neice
Your sisters daygter is your neice!