It's been said already but I will say it again - With something as legally binding as licensing, don't trust public forum as the truth, speak to Microsoft, speak to your Partner, speak to your Reseller they know the in's and out's of your companies agreements with Microsoft as you can have differences between other companies which make licensing on the public domain hard.
The following is my interpretation of the licensing guide
If you have Standard Edition and you are licensing VM's you have to license the VM OSE. So you have 4 virtual machines with 4 cores each, you need to purchase 16 Standard Core licenses
Licensing individual VMs is the only licensing option available for SQL Server 2019 Standard Edition
customers who are running the software in a virtualized environment under the Per Core model.
You cannot license hypervisor hosts under Standard Edition
If you are licensing Enterprise edition there are two ways
- License the individual VM OSEs
- License the actual HyperVisor Host(s)
Option 1, given the same example 4 VM's with 4 Cores = 16 Enterprise core licenses needed
Option 2, you need to ring fence some compute area just for SQL, so if you have 1 large Hyper-V / vSphere cluster, then all nodes and all cores need to be licensed, (6x32). If you create two Hyper-V / vSphere clusters (4 nodes in 1, 2 nodes in the other) and ensure all SQL VM's are spun up on the 2node cluster then you only need to license 2x32 as the SQL VM's cant move clusters, but can move nodes of the cluster. You cannot have a VM move from 1 host to another without licensing all the hosts in the cluster, so they all need to be licensed where SQL "COULD" be running from, you don't get an N-x discount on the unlimited virtualisation, its license all hypervisor nodes in the cluster as Enterprise or you license the VM OSE's as Enterprise.
Now your passive side, well that all boils down to having valid SA so you get mobility rights and passive rights (assuming they are truly passive, cold, idle), you still will need to ring fence compute just for SQL workload, you cannot have a 4&2 node hypervisor cluster in Prod and a 6node hypervisor cluster in DR as that's not like for like as you need to license the highest possible workload area, which if you didn't split DR out into 4&2 would still be 6x32 core licenses needed.
Pretty much if SQL can see it at either the VM or Hypervisor setting it has to be licensed accordingly.
Again just my interpretation of the licensing guide, don't take the above as truth, speak to your official partners