Custom meta values for single column

With the code below, I successfully created four columns to the existing columns for my custom post type post lists in the admin section. The columns were populated with meta_value(s) from their respective meta_key(s).

Now, I have been trying to create a single column (called Members Quorum - which is an addition of the last two columns above) instead of two. The value will be the sum of the meta_value(s) for both meta_key(s).

How do I go about this? Any clue?

Also, how do I also do the sum based on user roles and permission. In other words, some values will not be summed, if user does not belong to a certain role.

function columns() {

$columns = array(
'_my_creative_column' => array(
'label' => _('Create', 'cbi-tt'),
'type'=> 'post_meta',
'meta_key'=> 'shaping',
'orderby'=> 'meta_value',
'sortable'=> true,
'def'=> '',
),

'_my_design_column' => array(
'label' => _('Design', 'cbi-tt'),
'type'=> 'post_meta',
'meta_key'=> 'inspiring',
'orderby'=> 'meta_value',
'sortable'=> true,
'def'=> '',
),

'_my_members_column' => array(
'label' => _('Members', 'cbi-tt'),
'type'=> 'post_meta',
'meta_key'=> 'allmembers',
'orderby'=> 'meta_value',
'sortable'=> true,
'def'=> '',
),

'_my_quorum_column' => array(
'label' => _('Quorum', 'cbi-tt'),
'type'=> 'post_meta',
'meta_key'=> 'meeting',
'orderby'=> 'meta_value',
'sortable'=> true,
'def'=> '',
),

$columns = apply_filters ( 'cbi_tt_columns_bigworker', $columns );
foreach ($columns as $key => $col) {
$this->cols->add_column ( $key, $col );
}
}