That said, there are plugins that will allow you to embed Google docs. You could embed a Google doc and they could just update the doc, which would update automatically on your site when you load the page. Then they wouldn’t even need access to your website.

The custom template could output most of the page as usual, except for the editable table part. That part can be a separate post, page, custom field, anything that would be easier to edit than the full page of HTML. The template then fetches this data from where ever it is stored and outputs it in the proper position with appropriate formatting.

Instead of a page template, the table could be fetched from its normal location by a shortcode handler and returned. The shortcode is simply part of the normal front page content. The shortcode definition can be part of either a child theme or custom plugin.