If I knew the answer, I wouldn't have asked it!
Your grandfathers' sisters' grandchildren are your second cousins.
Children of sisters are first cousins. Grandchildren of sisters are second cousins. Great grandshildren of sisters are third cousins.
Some exact nouns for two children are sisters, brothers, brother and sister, cousins, sons, daughters, son and daughter, grandchildren, grandsons, granddaughters, etc.
Your grandmother's sister's grandchildren are your second cousins.
If you mean in the case of one of your parents re-marrying - the children of the new partner are your step-brother/sisters.
They all have children - Delois and Rodessa have grandchildren and great-grands. There is a documentary in the works featuring the Barrett sisters in a recent concert, as well as personal interviews with them and their children.
Some of your great grandpa's children are your grandparents. Their grandchildren are you, your siblings, and your cousins. Your great grandpa's other children are your grandparent's brothers and sisters (your great aunts and great uncles.) Their grandchildren are your first and second cousins.
I think he only had one brother although he lived with nine other children, maybe related.
bennelong had 7 sisters and 1 brother
You are a great-aunt.
If your friend's great grandmother was the sister of your great grandfather, then you are third cousins. The children of siblings (brothers and sisters) are first cousins. The grandchildren of siblings are second cousins. The great grandchildren of siblings are third cousins.
The spouse of your sister's brother-in-law is not related to you.