This is the only way we've been able to figure out how to get people to subscribe to calendars on an android device.  

First this part - which can only be done on a desktop machine or the desktop view of the ON Products/Ed Management Solution.

https://www.useloom.com/share/748ead9f5f864cb8bf9c7d2e92dc2bf3

Then this process on the actual Android device.

https://drive.google.com/file/d/1wA2kv1IrKM2hflqCBI0sy0aDCmKIJqPX/view

iPhone calendar subscription is much easier and can be done completely on mobile device. 

https://drive.google.com/file/d/197S-mX6rn0YQh1Jnky8RN6sXZqNAIKA9/view

If it's possible to get the subscription process on Android to match the iPhone/Mac process,  that would be ideal.