From the RG1 blade, click Deployments. You see a history of deployment for the resource group.
Reference:
https://docs.microsoft.com/en-us/azure/azure-resource-manager/templates/template-tutorial-create-first-template?tabs=azure-powershell

Explanation:
Not VM1 because it has BitLocker enabled.
Not VM2 because the OS disk is larger than 2TB.
Not VMC because the Data disk is larger than 4TB.
References:
https://docs.microsoft.com/en-us/azure/site-recovery/hyper-v-azure-support-matrix#azure-vm-requirements

Explanation
Ensure that "Enable an 'All Users' group in the directory" policy is set to "Yes" in your Azure Active Directory (AD) settings in order to enable the "All Users" group for centralized access administration. This group represents the entire collection of the Active Directory users, including guests and external users, that you can use to make the access permissions easier to manage within your directory.

Explanation:
Step 1: Stop VM1.
Step 2: Detach Disk1 from VM1.
Step 3: Start VM1.
Detach a data disk using the portal
* In the left menu, select Virtual Machines.
* Select the virtual machine that has the data disk you want to detach and click Stop to deallocate the VM.
* In the virtual machine pane, select Disks.
* At the top of the Disks pane, select Edit.
* In the Disks pane, to the far right of the data disk that you would like to detach, click the Detach button image detach button.
* After the disk has been removed, click Save on the top of the pane.
* In the virtual machine pane, click Overview and then click the Start button at the top of the pane to restart the VM.
* The disk stays in storage but is no longer attached to a virtual machine.
Step 4: Attach Disk1 to VM2
Attach an existing disk
Follow these steps to reattach an existing available data disk to a running VM.
* Select a running VM for which you want to reattach a data disk.
* From the menu on the left, select Disks.
* Select Attach existing to attach an available data disk to the VM.
* From the Attach existing disk pane, select OK.
References:
https://docs.microsoft.com/en-us/azure/virtual-machines/windows/detach-disk
https://docs.microsoft.com/en-us/azure/lab-services/devtest-lab-attach-detach-data-disk

Explanation
You can find unused disks in the Azure Storage Explorer console.Once you drill down to the Blob containers under a storage account, you can see the lease state of the residing VHD (the lease state determines if the VHD is being used by any resource) and the VM to which it is leased out. If you find that the lease state and the VM fields are blank, it means that the VHD in question is unused. The screenshot below shows two active VHDs being used by VMs as data and OS disks. The name of the VM and lease state are shown in the "VM Name" and "Lease State" columns, respectively.
Reference:
https://cloud.netapp.com/blog/reduce-azure-storage-costs