I am pretty sure when you select a tag it just backs them up in random order and there is no way to specify an order.  I think if you needed that you would want to select the VMs and then order them.

As per here - Step 5. Define VM Backup Order - User Guide for VMware vSphere

Chris,

We utilize VMware backup tags throughout our enterprise, it is much easier to manage.  I figured we would need to isolate the VMs in question and create a separate backup job for them.

Thanks

You could still use tags and have a job for each VM. Then schedule them to run after each other in order.   That would be a way around it.