Anyone,

Your parents raised your brother.  It is tragic that their son’s abusive behavior is directed toward them.  There is a saying, there are no victims, only volunteers.  Your parents are adults and have chosen to accept his behavior.  Unless your brother starts physically abusing them, then I don’t have any suggestions in changing their situation.  Of course, if you are going to try to convince anyone to change, it is not with your brother but with your parents.

Mark