Once you've decided on your names, it would be great if you'd start posting to social media.
You could write something like:
I’m part of Team X in the FileMaker Developer Challenge, along with [names of the three other people]. We’re looking forward to helping [Nonprofit Name] by creating the best custom app in the hackathon!”
If you have the time, you could accompany it with a composite photo of your team, put together in Photoshop. It doesn't have to be pretty -- just give a feeling of who your team is. Here's an example I just made. If you need to make the nonprofits’ names shorter, you could use: “NPHY” or “The Center, LV”