Hi Micromano,
I'd say that having one big website, rather than four smaller ones, is what I'd recommend also, combined with a really sound and solid website structure. Whilst authorship is less of a focus, I wouldn't remove any work you've done on that, as there've been mentions from Google staff that this may come back in the future. Re: branding, I'd say that it's incredibly important- if a company has a really strong 'About Us' page, which details experience and history and really demonstrates that your company is real and trustworthy, this will help both rankings and user trust (leading to greater conversion rates).
In response to your two questions about parent pages, I'd say the URL is less important. What's important is that you use the parent pages to build your site's architecture in terms of links. So, the homepage of your website should have clear, bold links to the 4 areas you cover, and your website's navigation should ideally be structured with 4 links, and maybe drop-down menus for the sub-pages of each area? If search engines can infer the structure of your site just by following your links, this will help (and will help users too!)
You should also make sure each of the 4 'area' pages is filled with rich information, and is structured as a landing page with general information, and links to the most important sub-pages.
In summary, site architecture is a lot more important than just the URLs of the site, I'd recommend you use good internal linking structures to indicate that your site is structured in this way.
Hope this helps!
Zoe