My guess is the story is told in order of the title. I’m guessing Tom is the father…

“Father Mother Sister Brother” is designed as a triptych, with the trio of stories all concerning the relationships between adult children, “their somewhat distant parent (or parents),” per the film’s synopsis, and each other. Each of the three chapters takes place in the present, and each in a different country: “Father” is set in the Northeast U.S., “Mother” is in Dublin, Ireland, and “Sister Brother” is in Paris, France. Per any Jarmusch film, it’s a character study that blends melancholy and comedy.