uncle and nephew
Second Cousin
Your grandfather's niece is a first cousin of one of your parents. Her son is your second cousin.
Your niece's son is your grand-nephew. You are the child's grand aunt, or grand uncle (whichever applies).
Your niece's son's son is her grandson. He is your great great nephew and you are his great great aunt or great great uncle, depending on your gender.
ther is a gramps a dad and a son
Great-niece.
your 2nd niece...!
Nephews and nieces
Your granddaughters and son have the relationship of nieces and uncle. Your granddaughters being his nieces and your son being their uncle.
boogey mans son boogey mans son
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
They would be great nieces or great nephews.