Filter meta request

Why don’t you use wp_query to retrieve posts. Its’s easy to include meta values in wp_query and a safe way to retrieve posts from wordpress database.

use this code to switch to the desired blog id and then after retrieving posts switch back to the original blog.

<?php
    /* 
       for global variables, since it is being changed or updated from time to time,
       please refer to Related Resources for more information
    */
    global $switched;
    switch_to_blog(2);
    echo 'You switched from blog ' . $switched . ' to 2';
      **//RUN WP_QUERY HERE**
    restore_current_blog();
    echo 'You switched back.';
?>

References:

Wp_query Codex

Switch to Blog Codex