Editing a post template

can you try changing these lines:

'order_by' => 'custom',
'meta_key' => 'Last Name',

in each of the above sections with this code:

'meta_query' => array(
    'relation' => 'AND',
    'last_name_sort' => array(
        'key'     => 'last_name',
        'compare' => 'EXISTS',
    ),
    'first_name_sort' => array(
        'key'     => 'first_name',
        'compare' => 'EXISTS',
    ), 
),
'orderby' => array(
    'last_name_sort' => 'ASC',
    'first_name_sort' => 'ASC',
),

(this is assuming that your first name key is ‘first_name’)