| Who is it? | Relationship to you | Common Ancestors |
|---|---|---|
| grandchild of your sibling | grandniece or grandnephew | your parents |
| grandchild of your first cousin | first cousin twice removed | your grandparents |
| grandchild of your second cousin | second cousin twice removed | your great grandparents |
| grandchild of your third cousin | third cousin twice removed | your great great grandparents |
| grandchild of your n-th cousin for n>3 | n-th cousin twice removed | your (n-1) times great grandparents |
Note that we could speak of zeroth cousins instead of siblings. A sibling relationship is exactly the same kind of relationship as is a cousin relationship. It's just that siblings are one generation closer than are first cousins. Similarly, a grandniece or a grandnephew is a zeroth cousin twice removed.