Is side-loading the app on each phone individually really my best option?
That depends on your definition of side-loading. Many people consider "anything other than the Play Store" to be side-loading, in which case the answer is "yes".
If you consider side-loading to mean by USB cable, you have alternatives. Put the APK file up on an Web server accessible from the devices, configured to serve up the APK file with the proper MIME type (application/vnd.android.package-archive
). Then, visit that URL in a Web browser on the device, which will trigger a download and optional install.
Or, use DropBox or similar services that have native Android clients, as they can do much the same thing.