You are out of synch with the common ancestor by 2 generations. It would be first cousins twice removed.
Your daughter and your sister's child are first cousins. Your daughter and your sister's grandchild are first cousins, once removed.
Your child and your great nephew's parents would be first cousins. Their children would then be second cousins. And if they have children, they will be third cousins.
Then you have a major problem
You would be second cousins.
They are of no blood relation. But they are cousins by marriage or 'step-cousins' as such.
First cousin once removed.
They are cousins.
I think the kids would be second cousins
Your granddaughter and your niece's son (the grandson of one of your siblings) are second cousins to each other.
cousins
Cousins?
No relation...lol