You can use the following JavaScript.

$(document).ready(function(){
  $(".no-dupe input").attr('data-parsley-duplicate-checker','');
  $(".no-dupe input").attr('data-parsley-trigger','focusout');
  $(".no-dupe input").attr('data-parsley-trigger-after-failure','focusout');
  
  window.Parsley.addValidator("duplicateChecker", {
	requirementType: "string",
	validateString: function(fieldValue) {
		let values = $(".no-dupe input").map(function() { return $(this).val(); });
        let existing = _.filter(values, function(value) {
            return fieldValue == value;
        });
      
    	return existing.length == 1;
	},
	messages: {
		en: "You cannot have duplicate approvers"
	}
  });
});

Just put a no-dupe custom CSS class on each of the fields you want to be unique.