Should one withdraw from the dining table when an abomination is committed by a brother who does not easily accept advice, and my disapproval of him might lead to a problem?

Do not abandon enjoining your brother simply because you assume it will not be effective. A Muslim is obligated to enjoin good and forbid evil, even if it does not appear to be outwardly beneficial. This is the view of the majority of scholars, while others have held that it is not obligatory if one believes it will be ineffective. If you believe that enjoining will lead to a greater harm than leaving it, then leave the gathering as long as he persists in the evil. The general principle is to leave a place of evil when one is able to, if it is not removed by enjoining, or if enjoining is impossible.