Do the apps depend on google play service? Do you hava a hint how the apps can be installed?
In addition to the Google Play Store option, if your users do not have access to this service I think you will find the following option helpful:
How To: Configure the Jive Android App For Enterprise Distribution
Jive Mobile Release Binaries
Jive for Android 4.1.1
As this will allow you to develop a custom mobile app which you can then distribute directly to your end users.
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