Your grandson and your brother's grandson are second cousins to each other.
Second cousins.
Your grandson is the great-nephew of your brother.
nothing
a relationship between brothers should be sacred and good....
First cousins
First cousins
Aunt and nephew
grandfather grandson.
If your daughter-in-law's grandson is a child from a marriage before she married your son, or after their marriage ended, her grandson is not related to you. If he is a child of the marriage between your son and your daughter-in-law, then he is your great grandson.
Shah Jahan was the grandson of Akbar.
Your father and your aunt are siblings (brother and sister) The grandchildren of siblings are second cousins to each other.
Your brother is your grandson's great uncle, and your grandson is your borther's great nephew. Some people would also say grand nephew and grand uncle.