As there are no blood ties there would be no relationship.
No relation...lol
Your mother's sister's children are your 1st cousins.
Your daughter and your sister's child are first cousins. Your daughter and your sister's grandchild are first cousins, once removed.
Your sister's son and your daughter are first cousins to each other.
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.
Your son and your mother's sister are in a "Great Nephew/Great Aunt" relationship.
They would be cousins, once removed.
Your daughter and your sister's son are first cousins to each other. Your sister's son's daughter (her granddaughter) and your daughter are first cousins, once removed.
Your aunt's sister is either your mother or another aunt. Therefore, her children are your cousins. If her sister is your mother, then those children are your siblings. If she is another aunt, then they remain your cousins.
Your cousin's sister is also your cousin. Your first cousin's children and you children are second cousins. Your second cousin's children and your children are third cousins. And so forth.
The grand children of your granmother's sister are your Second Cousins because you share one or more great-grandparents.
If your sister-in-law is the sister of your spouse, her son is not related to your sister's son. If your sister-in-law is the wife of your brother, her son and your sister's son are first cousins.