$group1 = new WP_Query(array(
'post_type' => 'oral_histories',
'posts_per_page' => -1,
'meta_key' => 'last-name',
'orderby' => 'meta_value',
'order' => 'ASC',
'meta_query' => array(
'relation' => 'OR',
array(
'key' => 'last-name',
'value' => '^A',
'compare' => 'REGEXP'
),
array(
'key' => 'last-name',
'value' => '^B',
'compare' => 'REGEXP'
)
)
));