I second, or third?, the notion that you should more than likely only have a single WordPress installation. It definitely would increase the maintenance involved. Take everything you should do to maintain an installation, then double it. I'm certain everyone in your organization could do without that.
But if your organization is willing to endure the duplication of effort, there are other things to be concerned about. Not every theme is created equal. Some themes are faster than others, some are more secure than others and most themes will differ in every other way. So one theme could be a hindrance, while the other at least pulls it's weight.
In regard to the subdomain blog or subfolder blog question, there was a time in recent history where I would have said it didn't matter. Supposedly the link equity/juice flows just fine either way. However, someone in Moz Q&A made a very good point. To paraphrase EGOL; "Algorithms change, if you install your blog on a subfolder you will always be right."
I'm not sure when your company made the jump to WordPress, but WordPress has had the ability to display static pages for years. My first agency used to run a combination of CMS Made Simple and WordPress, I think it was due to the page handling issue. That was over six years ago. They later made the jump to full WordPress about five years ago.
So it sounds like the site isn't properly configured for your purposes. Here is how you should handle that, direct from the WordPress codex. From there you can setup your site's page structure through parent/child relationships. So if you're selling widgets, your structure may look like:
**Page Hierarchy **
site.com/widgets/
site.com/widgets/blue-widgets
site.com/widgets/red-widgets
Posts Hierarchy
site.com/blog-diggety/
site.com/blog-diggety/sweet-post
There are Pages and Posts. You bring the hierarchy. And speaking of which, should you change your site URL structure, you will definitely want to research 301 redirects.
To me, there's no question in my mind. You should stick with one WordPress install. Hopefully that helps.