Sexual
Your great uncle's niece could be your mother, or your aunt. It is also possible that she is not related to you at all, as you might not share a common ancestor.
Your aunt is your child's Great Aunt, so your child is her great niece or great nephew.
She would be your great aunt.
The great aunt is the great niece's baby's great-great aunt.
Removes, whether once, twice or more, never apply to uncles or aunts, only to cousins. You can have great uncles and great great uncles, etc.
Auntie is the usual spelling, but aunty is a variant.
Presuming your son is also your wife's son, the your wife's aunt is your son's great aunt and he is is her great nephew.
When one person's great grandmother is the another person's great aunt, the relationship between the two people is that of second cousins, once removed.
Your grandfather's brothers would be the uncles of your parent. That would make them your great uncle.
Since your mother and her sister have thesame aunts and uncles, your mother's sister's aunt is your grand aunt or, as some sat, your great aunt.
Your great-aunt
You Aunt is you grandson's Great-Great Aunt. Your grandson is your Aunt's Great-Great Nephew.