Thank you for taking the time to help.
Problem: I have such a difficult time defining ‘themes.’
Background: In my short story, each family member does something self-indulgent. For example, dad drinks excessively, son eats too much candy, mom exercises excessively. Overall, each family member has a vice that they turn to for pleasure.
Question: What is my story’s main theme? Pleasure? Self-indulgence? Vices? How would I define it? Please note, this short story may turn into a short film. Not sure if that matters.
Almost all of these becomes your themes. As these are just assumptions, when you show them through the character’s conversation, these assumptions become arguments and hence proved. Therefore, they become permanent thematic strands.