In searching for this topic, it doesn't appear when using the "Start Approval Process / Everyone must approve" that there is an easy way for an end user to see who has or has not approved a request (if you have say, 4 people in the Assigned to).
About the only way I can think of doing this would be to setup parallel branches with one assigned to in each branch. I can have 1, 2, 3, OR 4 approvers, so I'll also have to add some conditional logic to see if each one has a value and act accordingly. I will then update a column in the list for each approval status ("Approver status 1", Approver Status 2", etc.).
Hard to believe they don't have something for this OOTB just to see the status of each approver (by the end user without a premium license).