Your daughter and your brother's child are first cousins to each other.
Your daughter and your brother's granddaughter are first cousins, once removed, to each other. The "once removed" refers to the fact that they are separated by one generation if you count from their common ancestor, your parents.
If you really need a relationship term, use granddaughter-in-law. Most people would merely say "my grandson's wife."
Your sisters grandson would be your grandnephew.
nothing
Your granddaughter and your sister's grandson are second cousins.
Your brothers great granddaughter is your great great niece.
Your grandson and your sister's grandson are second cousins to each other.
they would be first cousins once removed. this is because the grandchild's parent would be your son's first cousin and because its the cousin's child, its once removed
granddaughter
Second cousins.
Granddaughter
Your daughter's son is your grandson and you are his grandparent.
My daughter's husband is my son-in-law, so is my granddaughter's husband my grandson-in-law? Pat