Your sister-in-law is either the sister of your spouse or the wife of your brother.
The parents of the sister of your spouse are also the parents of your spouse and so are your mother-in-law and father-in-law.
The parents of the wife of your brother are not related to you.
For a female grandchild to your sister/brother: great niece
For a male grandchild to your sister/brother: great nephew
He would be your brother-in-law.
Great grandniece or great grandnephew
They would be cousins to some degree. They are 2nd cousins.
The common ancestor is your parents. Your children and your sister's children are first cousins. Your grandchildren and your sister's grandchildren are second cousins. Your great-grandchildren and your sister's great-grandchildren are third cousins.
No, they`d be the second sisters great nieces and nephews
You brother is your grandchildren's great uncle or granduncle.Your grandchildren are your brother's grandnieces and grandnephews
The relationship term is usually hyphenated "great-grandchildren" (grandchildren's kids).
they would be second cousins
Your father and your aunt are siblings (brother and sister) The grandchildren of siblings are second cousins to each other.
Your grandchildren and your grandniece are second cousins to each other..
Your sister's children's children are her grandchildren.Your children and your sister's grand children are first cousins, once removed.Your grandchildren and your sister's grandchildren are second cousins.
Your sister is the great-aunt (also written great aunt) of your granddaughter.