Can you have a relationship with your Sisters Daughters Daughter?

Answer 1

Your grandmother's sister's daughter's daughter is your great aunt's granddaughter and your second cousin. You can have a relationship with anyone your want. You can't marry your first cousin in may (but not all) US jurisdictions, but no jurisdiction forbids marriage between second cousins.

Answer 2

Your mother's sister's son is your first cousin. Marriages between first cousins have not been uncommon in some ethnic groups, including European descended groups in parts of North America.

Lesser relationships are therefore certainly acceptable.

Remember, friendship is a relationship, too.

Answer 3

Your dad's sister's son's daughter (your dad's sister's granddaughter) is your dad's great niece and your first cousin, once removed.