Firstly I should write who are these two characters, so as a protagonist I would mark Berenice, she is the one who wants to safe family heritage and against here with another opinion is Boy Willie, who wants to sell it. The main thing they are fighting for is the old piano. Berenice wants to save it because it means a lot for her, but Boy Willie needs money, so he wants to sell it to make money out of this business.
They play off of each other by making arguments about why sell or why not to sell the piano. I think that mostly it is Berenice who is talking, who have to say something about it, she want to persuade Boy Willie to believe that this piano means a lot for the family, but Boy Willie still repeats that he wants to sell it and no other facts are important for him, he does not care about the past of the piano and its story. So those are the two main characters who are against each other. What concerns other characters, they are not really on a one side or on the other, they do not say to sell in or not to do it. I think that they are not antagonist or protagonist because they are somehow neutral, they do not seem to care about this business and this fight between Boy Willie and Berenice.
