Pagination for multiple queries merging into one Loop

Firstly you need to merge your two query into one,
and need to use WP_Query instead of get_posts:

$paged = 1 ;
$posts_per_page = 10 ;

$args = array(
    'post_type' => 'espresso_event',
    'meta_key'  => 'event_start_date',
    'orderby' => 'meta_value',
    'order' => 'ASC',
    'posts_per_page' => $posts_per_page,
    'paged' => $paged,
    'meta_query' => array(
        array(
            'key' => 'event_registration_end',
            'value' => date('Y-m-d'),
            'compare' => '>='
        ),
        array(
            'key' => 'event_registration_end',
            'value' => date('Y-m-d'),
            'compare' => '<='
        )
    )
) ;

$query = new WP_Query($args) ;
if ($query->have_posts()) {
    // Here our parameter:
    $total = $query->found_posts ;
    while ($query->have_posts()) {
        $query->the_post() ;
        // Do something like
        ?><h3><?php the_title() ; ?></h3><?php
    }
    echo '<div id="pagination">' ;
    $next_link = '' ;
    $prev_link = '' ;
    if ($paged > 1) {
        if ($paged-2) {
            $prev_link = add_query_arg(array(
                'paged' => $paged-1,
            ),get_permalink($post->id)) ;
        } else {
            $prev_link = get_permalink($post->id) ;
        }
    }
    if (($total/$posts_per_page) > $paged) {
        $next_link = add_query_arg(array(
            'paged' => $paged+1,
        ),get_permalink($post->id)) ;
    }
    if ($next_link) {
        echo '<a href="'.$next_link.'" class="next">Next Page</a>' ;
    }
    if ($prev_link) {
        echo '<a href="'.$prev_link.'" class="prev">Previous Page</a>' ;
    }
    echo '</div>' ;
} else {
     echo 'Sorry, there is no post etc' ;
}

Not tested, but your need must be something like this.