Showing Group in Admin

Hello. I really like your plugin and does everything I want it to do so far!
However, my client has asked if they can see the group name in a new column in the admin area. I’ve added it ok in the sorting page, but in the first admin page that just lists the staff, I can’t seem to display it! The code I have used goes like this:

add_filter( "manage_staff-member_posts_columns", "sslp_staff_member_custom_columns" );
function sslp_staff_member_custom_columns( $cols ) {
	$cols = array(
		'cb'				  =>     '<input type="checkbox" />',
		'title'				  => __( 'Name' ),
		'photo'				  => __( 'Photo' ),
		'_staff_member_title' => __( 'Position' ),
		'_staff_member_email' => __( 'Email' ),
		'_staff_member_phone' => __( 'Phone' ),
		'_staff_member_group' => __( 'Group' ),
		'_staff_member_bio'   => __( 'Bio' ),
	);
	return $cols;
}

But of course I don;t think the ‘_staff_member_group’ bit is correct!

Could someone please advise how I can include this in the back end?

Many thanks!

https://www.ads-software.com/plugins/simple-staff-list/