As Milo said :
$query->set('meta_key', 'wpcf-object-sold-status' );
$query->set('orderby', array('meta_value' => 'ASC', 'date' => 'DESC'));
// $query->set('order', 'ASC DESC' ); // not needed
Relevant link: https://make.wordpress.org/core/2014/08/29/a-more-powerful-order-by-in-wordpress-4-0/