If you're open to using different types of GUIs I can help you make a custom GUI that has multiple text fields where the user can enter text. Or, if you have to use JOptionPane, you'll have to wait and see if this is possible - maybe someone else here knows how to do it. Let me know.
No, it doesn't necessarily have to be a JOptionPane, but that was the easiest way when I was only taking one input text field, because of the showInputDialog option. I did see that suggestion about using an array for message, but I couldn't figure out how to get it to work. Could you give me an example of what they mean