SQL Server 2014 SP2 upgrade on Alwayson + FCI
The answer can be found here: https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/upgrading-always-on-availability-group-replica-instances
I've used this method several times on 2 and 3 node AlwaysOn Availability Group implementations, and it works very well, and is explained in great detail in the above link.