IIRC, FWIW, the brother of one’s grandfather is one’s great uncle. We go through that in my own family, where I have two grandkids (stepgrandkids, technically); but my wife’s brother and sister are called uncle and aunt by the grandkids, even though they are actually uncle and aunt to my stepson.
IIRC, FWIW, the brother of one’s grandfather is one’s great uncle. We go through that in my own family, where I have two grandkids (stepgrandkids, technically); but my wife’s brother and sister are called uncle and aunt by the grandkids, even though they are actually uncle and aunt to my stepson.