Custom MySQL Query for Post and Post Meta

You have to use JOIN for that. Try it like this:

$wpdb->get_results("SELECT tags.*, $wpdb->posts.*, $wpdb->postmeta.*
              FROM tags
              INNER JOIN $wpdb->posts ON tags.charity_id = $wpdb->posts.ID
              INNER JOIN $wpdb->postmeta ON tags.charity_id = $wpdb->postmeta.post_id
              WHERE tags.charity_id = $charity_id"
            );