A Step Braduncle extended is a Step-Brother-Dad-Uncle. It happens when your mother's mother marries your divorced father so you and your mother are now step sisters and your grandmother in law is now your mother and then you marry your sister-mother and have a child and now the child is your "Brother- Son- Step- Nephew"
Friend: hey bro u know where i can score some lean for the rager tonite?
Friend 2: yeah bruv the plug got in this new Broncleer shit from south Africa it be hitting different!
when your brother is also your uncle either because your mother had a child with your grandfather or your father had a child with your grandmother: the male offspring being your brother; because you share one parent, and also your uncle; because he is the child of your grandparent as well
I have seen many explanations of this, but here I will explain how it works:
A chav girl has sex with her chav brother, who is also her father which is not uncommon. They produce a chav child, which will biologically be both her brother and her son. At the age of about 8, the chav child will have sex with it's chav mother afore mentioned 'chav girl', producing another child to which the previous chav child will be brother, uncle, and dad.
chav: im gona see ma datonight.
chav#: e's ur uncle too rite?
chav: yeah an my bro. e's my bruncledad.