Your sister's husband is your brother-in-law. Your brother-in-law's brother is not related to you and neither are his children. But he is your sister's brother-in-law and his children are your sister's nieces and nephews.
a relationship between brothers should be sacred and good....
The cast of Between Two Husbands - 1922 includes: Jean Gabriel as Twin Brothers Arline Pretty
There is no relationship. You do not share a common ancestor. The connection is simply through marriage.
They were brothers.
brothers
They are brothers.
step brothers
It is no different than the relationship between straight parents and their children.
Brothers
ya mum!
They are brothers
The children of two brothers who marry two sisters are first cousins to each other. Some people like to describe the relationship as "double cousins" since most people have cousin relationships through one parent/sibling pair, and these have it through two such pairs.