VMs will consume the C drive if that is the allocated drive for storage. The SRP (Storage Resource Provider) will need to allocate space for the disks of the VMs. As they are fixed sized .vhd files, they will consume the entire 128gb size upon VM creation.
Upon VM deletion, the .vhd file will typically stay until the storage account or file is deleted. Typically a VM and all its associated resources will sit in the same resource group, so deleting the resource group will fully delete the VM.
When in the Tenant Portal, you will not be able to see VMs created in the Admin portal. Tenants do not have access to the admin VMs or resources. This is by design, and so that subscriptions can only see their own resources similar to the Azure portal.
Please let me know if you have any other questions.