Although I have no experience with it, NetlifyCMS is one option. It just requires the use of GitHub.
Another option is to let your communications people use a web-based git repository browser, such as GitHub, BitBucket or Gitlab. Then, let them edit HTML or Markdown source directly from there.
Lastly, people on Hacker News mentioned the use of a shared network drive that allowed marketing people to edit source files and review changes on an always running dev server instance. After marketing people were done with changes, git commits and pushes would be managed by developers. If you have a slightly larger team, this could be an option, as well.
Hope this helps.