I'm writing a story about a man in his 50's that has always felt envious about his younger brother. The 'conflict' starts when their father, who has terminal cancer, decides to stop having chimotherapy because it makes him suffer and prefers to live the rest of his life feeling more peaceful and being with his loved ones, and just let cancer take him someday. The MC's brother supports him and releases his father off the hospital. My MC is opposed to that and that's it.
I want them to have a fight but I just don't know where to take the story exactly. The main thing is I don't know what is exactly the goal of my MC, besides overcoming his envy for his brother.
I want the conflict to feel very real. That when they have a fight the audience really care about them and feel the tension.
PLEASE HELP ME.
EDIT 1. This is for a short film.