How to return multiple arguments from AJAX callback function

Have you tried returning an array instead?

wp_send_json($an_array_of_your_vals);

And then parse the array in the success function?

success: function( data ) {
   var obj = jQuery.parseJSON(data);

   if( obj.arg_1 ) {
            $('selector').append( obj.content );
   } else if( obj.arg_2  ) {
            $('other_selector').append( obj.content );
   }
}