Your granddaughters and son have the relationship of nieces and uncle. Your granddaughters being his nieces and your son being their uncle.
Your son and your first cousin's granddaughter are second cousins, once removed, to each other.
Your granddaughter could be your son's daughter, or your son's niece.
Your son and your sisters child are first cousins. The granddaughter is out of synch by a generation. That will make them first cousins once removed.
Your granddaughter and your niece's son are second cousins.
Your granddaughter and your sister's grandson are second cousins.
step-granddaughter
Your aunt is great great aunt to your son's daughter (your granddaughter). Your granddaughter is your aunt's great great niece.
It depends - he could be either her son or her nephew.
There is no relationship. The two of you do not share a common ancestor.
If you are a woman, you are your great grandmother's great granddaughter so your son is the son of her great granddaughter. But there are other possible relationships to other of her great granddaughters.The great granddaughter could be your sister. Then your son is her nephew and she is his aunt.The great granddaughter could be your first cousin. Then she and your son are first cousins, once removed.The great granddaughter could be your second cousin. Then she and your son are second cousins, once removed.
you are an aunt or uncle of the sun
Your daughter's son is your grandson and you are his grandparent.