Anyway, whatever you are up to with the loop so far is not specific to multisite. You may find more help in the themes and templates forums rather than multisite for your theme designing.
You say, “I can get posts to appear in DESC order. But only if the Landing Page is posts”
That is the way it is supposed to work(DESC by post date) Landing on a static page does exactly that -display one page.
Your index.php snippet:
Adding a “$query” var, and then doing nothing with the var of course does nothing.
Perhaps syntax like the following would make more sense:
<?php $query = new WP_Query( array ( 'orderby' => 'title', 'order' => 'DESC' ) ); ?>
<?php while ($query->have_posts()) : $query->the_post(); ?>
<!-- Do stuff... -->
<?php endwhile; ?>
(Your snippet loop above descends by alphabetical order descending Z-A by the way).
At any rate, editing the index.php – if your parent theme has a static page template “page.php” in the template hierarchy – indeed does nothing. You need to figure out which template page you are viewing your static page with and edit there.
For example, a twentytwelve child theme would display a page using the loop found on the “page.php” – so the child theme would need edits to a corresponding “page.php” (or “content-page.php” if you are editing the Loop only and “front-page.php” if landing on the front page).