Reading your question I assume both approvers have the same userrole?
In that case the easiest will be to put your tab container in a dataview, which has a new helper entity as data source.
This entity should have two booleans: showTab1 & showTab2.
Upon opening the page with the tab container, you can create an object of the helper entity. In this flow you check which user is currently logged on and based on that you can set the correct boolean to true.
On the tabs you can then set visibility to: $helper/showtab1 = true & $helper/showtab2 = true
Hope this helps
You are able to apply visibility to tabs based on roles
Have a look here to see how.