I would think this code (copied from above) using the forumbit_display hook should work:
Code:
$template = vB_Template::create('ad_board_inside_forum_listing');
$template->register('forumid', $forumid);
$forum['board_inside_forum_listing'] = $template->render();
but I assume that 3rd line should be $ad_location['board_inside_forum_listing']. Yes, you can render a template more than once, so it should work. I don't see offhand why it's only displaying in the first line. Are you seeing the 2 forum id numbers from the first two lines in your template? Are you sure they're all using the level2 forumbit template?