Who is the Antagonist for August Osage Country?

August: Osage County is a dramatic comedy play written by Tracy Letts. The entire story takes place within the month of August inside the home of Beverly and Violet Weston, who live in Oklahoma. Letts' portrayal of the Weston family is such that one key protagonist and one key antagonist are hard to identify; multiple characters can be argued to fit into each role. However, generally speaking, Violet, the matriarch of the family, is often considered to be the story's antagonist, while Barbara, her oldest daughter, is typically considered the protagonist.
From the start of the play, Violet Weston is a generally unpleasant person. Because she is addicted to prescription drugs and prone to unkind rants (such as the one she gives at her husbands funeral dinner), other members of the family find it difficult to deal with Violet. Her addiction to prescription drugs is complicated by the fact that she is fighting oral cancer at the time of the story.
Throughout the play, Violet fights to keep the money her children were meant to inherit from their father's death. She continually insults, taunts, and offends her family members, causing them to decide to address her addiction. Barbara, her eldest daughter, leads the charge in searching the home for all of Violet's pills.
By the end of the play, no real progress is made in terms of the familial relations. The story ends with Barbara and Violet in one final confrontation, as Violet blames her daughter for the death of her husband. Barbara, seemingly realizing that there is nothing more she can do to help her mother, leaves her with her live-in caretaker.