#states on exposed filter form
Though you have custom solutions in place, but a try for views_dependent_filters can be worth, this might be hint as well for your custom solution.

views_dependent_filters module:


  Allows the presence of exposed filters on a view to be controlled by
  values in another exposed filter. Dependent filters are hidden when
  not relevant, and their values are not considered when the exposed
  form is submitted.
  
  The module is compatible with both the Views basic and the Better
  Exposed Filters form plugins.