I would explore creating a different Request Status ('state') and only push the case to 'Approved' when the correct status is met. To do this, you will likely need to create a new UI Action and display that on your form (and hide the current UI Action that "approves" the case, until the request status is correct). 

For example:

• Form #001 is submitted and routed to Group A for approval. The case is in "Awaiting First Approval" state and the Approval is "Requested." Group A clicks "Approve Case" and the state changes to "Awaiting Second Approval." 
• Form #001 is now routed to Group B for approval. Because it is in "Awaiting Second Approval" state, the UI Action to "Close" the case appears. When this "Close" button is clicked, the case status (state) changes to "Approved" and the Approval changes to "Approved."

You could also modify the flow directly to change how the routing works! There are a bunch of different OOTB "Approval" choices that you can utilize.