@ericgauvin Although the default wordpress_sites list has just one site, you may list multiple sites/subdomains for your DO droplet. The list is per environment, so the idea is that if a given Trellis project has multiple sites, the staging versions of those sites will go on one DO droplet and the production versions of the sites will go on a separate DO droplet.
However, it sounds like your goal is to put a given site’s staging and production versions on a single DO droplet. You can do so, but you’ll have to adjust your Trellis setup slightly. See if these tips help (and this).