Your uncle's great granddaughter is your first cousin, twice removed.
I believe they would be great aunts or great uncles.
Your mothers sisters Granddaughter is your second cousin
You would be 2nd cousins, assuming that the brother's wife's granddaughter is also the brother's granddaughter. If the granddaughter is not the granddaughter of the brother, there is no relationship.
Your grandson and your sister's grandson are second cousins to each other.
Your sisters grandson would be your grandnephew.
That person would be either me or my sister...if the cousin of me great uncle was my great grandfather. If the cousin was another of my great uncles, then the person would be my cousin. Example 1: My dad has a brother who is my uncle. That uncle has a father who is my great uncle. If his father or mother had sisters or brothers who had kids, these kids would be cousins to this great uncle. one of them could be my grandfather. so my grandfather's granddaughter would be me if I am a girl or my sister if I am a boy. Example 2: In any level of the family tree there can be cousins...children of my uncle or aunt. when they have kids they are second cousins...children of first cousins. If these second cousins have kids, they all are third cousins. So since my great uncle had a cousin which was 2 generations above me...the next generation would be second cousins and the third generation would be third cousins. If my grandfather was not the cousin in question, then the cousin would be someone else on the same generation level, 2 levels above me and the granddaughter would be on my level and therefore my third cousin.
If you really need a relationship term, use granddaughter-in-law. Most people would merely say "my grandson's wife."
She would not be. You uncle's children are your first cousins and his grandchildren are your first cousins, once removed. Your children and your uncle's granddaughter are second cousins to each other.
Your 1st cousin's granddaughter would be your daughter's niece.
Your grandfather's brothers would be the uncles of your parent. That would make them your great uncle.
You would be his Great Uncle or Great Aunt He in turn would be your Great Nephew.
If your great great uncle (the brother of your great grandparent) had a great great granddaughter, you would be third cousins, once removed.