In every human sibling pair, it is inevitable that one will become the "good one" that tries to outshine the rebel. Same goes for dog siblings. According to the dog's owner, Derick Duffner, if you tell Luke to fetch his brother Jack, that's exactly what he'll do.
Bro drags him by the collar! If you did this to your own brother it would be considered child abuse, but when this dog does it, it's ADORABLE.