Well, there's a lot wrong with "drengen er mine brører."
For one "brører" is not a Danish word. Maybe you meant to write "brødre", which is the plural of "bror"?
Second, "drengen" is singular and "mine" is a plural possessive. They don't match grammatically.
I think you were trying to write "Drengen er mine brødre." which would translate to "The boy is my brothers." which doesn't make much sense.