I gotta side with the brother, actually. I will agree that SHOOTING might have been an over-reaction, but you said yourself that he has told you many times to keep the birds off his porch. Wandering livestock is just as big of a hazard as wandering dogs.
Did you know that if your chicken gets into the street and someone swerves to avoid it that YOU are liable for all the damages?? Up to and including if someone is killed??
There was a person here a few years ago, her neighbor moved away, leaving behind their free-range flock of guineas. She felt sorry for the birds, so started to occasionally put out food for them in the winter. They were in the road one day, someone swerved, over-corrected and flipped their car. All told, she was on the hook for over $75,000 in damages. AND SHE DIDN'T EVEN OWN THE BIRDS!! But, because she had taken on the task of caring for them, she was considered to be the owner legally.