Call the great nephew Joe and the great aunt Pamela.
If Pamela is the sister of Joe's grandmother or grandfather, then Joe and Pamela are "blood relatives."
However, Pamela could be the wife of a brother of one of Joe's grandmother's or grandfathers and still be Joe's great aunt. In that case, Pam and Joe are not "blood relatives."
They can be, but they are not necessarily so. I can have grand nephews and nieces who are the grandchildren of my brother (my sibling), and I can have grand nephews and nieces who are the grandchildren of my wife's sister. These two sets of nephews and nieces are not blood related. When you visit your aunt and uncle (married to each other) you are related to only one of them by blood. They are still your aunt and uncle.
Your grandchild and your nephew are 1st cousins once removed.
Your great niece and your great grandson are second cousins, once removed.
Your Great-Aunt/uncle, would be your parent's aunt/uncle.
So, your grand nieces would be your nieces kids, and plus their kids would make you their Great-Great-Aunt/Uncle.
2nd cousins?
no
They are your grand-nephews and grand-nieces or great-nephews and great-nieces.
They are your great nephews and/or great nieces. Alternately, some people say grand-nephews, grand-nieces.
Some would call your nephew's children your grand nephews and grand nieces, others would call then your great nephews and great nieces.
Your nephew's children are your great nephews and great nieces (or grand nephews and grand nieces).
The vast bulk of it went to nieces, nephews, grand nieces and grand nephews. Anthony Dion Fay received only $5,000, according to Victoria Wilson.
Your mother's nieces' children are your mother's grand nephews or grand nieces. They are your first cousins, once removed.
Mate: Sandstorm Daughters: Squirrelflight, Leafpool Father: Jake Mother: Nutmeg Sister: Princess Half-Brothers: Scourge, Socks Half-Sister: Ruby Nephew: Cloudtail Grand-Nieces: Whitewing, Amberkit Grand-Nephews: Dewkit, Snowkit Great-Grand-Nieces: Dovewing, Ivypool Grandsons: Lionblaze, Jayfeather Granddaughter: Hollyleaf
Antigone and Ismene are the sisters of the twin brothers Eteocles and Polneices. All four are the children of Theban King Oedipus, and both the children and grandchildren of Theban Queen Jocasta. All four also are the nieces and nephews, and grand nieces and grand nephews, of Theban King Creon, who is Jocasta's brother. All five are descended from Cadmus, the founder and first Theban king.
You would be their great-granduncle or great grand aunt, and they are your great-great nieces or great-great nephews.
The English language has no collective term that would cover both nieces and nephews, other than the general word "relatives." According to Merriam Webster & Wikipedia; 'niblings' (play on siblings) is a collective term for nephews and nieces.
Your nephew's child is your great niece (if a girl) or your great nephew (if a boy).
Grand niece.