Sorting posts by multiple values, combined

I’m not entirely 100% on the order you are looking to achieve, but I think you need to spend a little more time with the documentation for WP_Query. An orderby array takes the name of a column in the wp_posts table OR meta_value or meta_value_num as the key, not the name of the custom field key (custom_key in your case). The actual name of the custom field is defined in the args array as meta_key.

If you look at the last two examples under Orderby Parameters in the Codex, you can see how this works and apply it to your situation. This is untested but gives you the general idea:

$args = array(
    'posts_per_page' => 30,
    'category__in' => $idObj,
    'paged' => $paged,
    'meta_query' => array(
        array(
            'key' => 'original_act_ordinance_information_0_act_ordinance_number',
            'compare' => 'EXISTS',
            'type'    => 'NUMERIC',
         ),
     ),
     'orderby' => array(
         'title' => 'ASC',
         'post_date' => 'DESC',
         'meta_value_num' => 'ASC',
     ),
     'meta_key' => 'original_act_ordinance_information_0_act_ordinance_number',
 );

You also had your meta_query set up incorrectly so I suggest you review that part of the WP_Query docs as well.