To see your brother-in-law in your dream represents characteristics in him that you find within your own self. Consider also your waking relationship with your brother-in-law. If you dream that you are arguing with your brother-in-law, then it suggests that you are refusing to acknowledge or accept certain of his qualities.
To see your brother-in-law with his arm in a sling in your dream implies that he is being unhelpful or unproductive. If he is wearing a suit, then it means that you are underestimating his abilities.