Your specific needs might vary -- for instance, perhaps you need subject matter expertise in your writers, or coding experience from your long-form content creators. Or perhaps your titles differ, and your "content creators" are actually "content strategists", or your "social media manager" is really a "specialist." Make edits as you see fit, but these frameworks should be helpful in getting you started if this is your first time hiring for any of these positions.
With the pace of social media and the frequency of blogging, not to mention that many of your content assets will be used across multiple campaigns and teams, a lightweight project management tool is critical. I recommend using a free software called Trello, which helps you organize your content, set deadlines, attach files, and collaborate with multiple teammates. Another great tool for keeping content projects organized from planning to publishing is Zerys -- a content marketing tool with a built-in marketplace of professional writers.
Predictably, blog posts are typically written by the bloggers. However, if your team is large enough to have someone dedicated to creating gated assets and premium content -- things like ebooks and tools -- they should also write blog posts to help promote those assets. SEO specialists will also work closely with bloggers, as blog posts are often a company's best opportunity to improve organic search rankings. As such, bloggers should be writing posts that help improve the site's SEO, and drive organic traffic and leads. Their editorial should be informed by keyword research, and optimized for SEO.