Page template for a site from network

You could use the filter theme_page_templates present since 3.9.0 like so:

function my_theme_page_templates( $page_templates, $this, $post ) {
    $travel_blog_id = 2;
    $blog_id = get_current_blog_id();

    if($blog_id != $travel_blog_id) {
        if(isset($page_templates['page-travel.php'])) {
            unset($page_templates['page-travel.php']);
        }
    }

    return $page_templates;
}
add_filter( 'theme_page_templates', 'my_theme_page_templates', 20, 3 );