Great grand niece
Grandchild
Half aunts and half nieces typically share about 25% of their DNA. This is because the half aunt is the sister of one of the niece's parents, meaning they share one parent in common. As a result, the genetic relationship is similar to that of a grandparent and grandchild.
your grandchild
your great grandchildren
Your granddaughters and son have the relationship of nieces and uncle. Your granddaughters being his nieces and your son being their uncle.
Great niece or nephew.
Your daughters are great aunties if their nieces have kids. Your daughters kids are your grand children.
He is their Uncle and they are nieces and nephews.
Second cousins.
Second cousins, once removed.
Your brother's children would be your nieces and nephews.
Your brother-in-law's children are your nephews and nieces.