You can also develop one or more of these as a plugin to your main app, in the form of a separate APK available for download. That APK would expose some component that the main app would use — since I do not know the nature of your integration with these services, I cannot make a more specific recommendation about that. You would use your own signature
-level custom <permission>
to secure communications between the two apps. And, as a bonus, if using the third-party library adds requirements for additional permissions, you would only need those permissions in the plugin APK, keeping your main APK smaller.