If you are referring to YOUR grandmother and grandfather then your children are their great grandchildren. If you are referring to your parents, then your children are their grandchildren. The primary kinship dominates.
The children of your grandmother and the children of her brother (your great uncle) are first cousins to each other.
Your children and great uncle's children are first cousins, twice removed, to each other.
If the grandmothers of two people were first cousins to each other, then the two people are third cousins to each other.
The grandchildren of one of two first cousins are third cousins to the grandchildren of the other.
Second cousins, once removed.
Hopefully, women who are grandmothers of the same children are friends, but in western culture they are not otherwise related. They are the mothers of the parents of the children
brothers
a relationship between brothers should be sacred and good....
There is no word in the English language for a relationship between grandmothers of related grandchildren
Your ancestors are the people whose children lead eventually to you. They are your mother and father, grandmothers and grandfathers, great grandparents, great great grandparents, etc. Your cousins are the children, grandchildren, great grandchildren, etc, of the brothers and sisters of your ancestors.
They were brothers.
They are brothers.
brothers
step brothers
ya mum!
Brothers
Zeus and Hades are brothers.