These stills are meant to be reconstructions of ancient burial mounds from right after they were constructed in neolithic times, which is why there’s no grass.
These look very good, and certainly very descriptive. It’s entirely up to you whether you wish to depict them “as very-recently constructted” or “following the passage of time.” And, actually, for a project such as this I would probably opt for the former.
All of these images show excellent mood, use of “mist” and so-forth. So, quite honestly, I would just “call them ‘[very] good’ [for now],” and move on to other elements of the overall project.
Try to bring all of the major elements to more-or-less this level of completion. This will greatly relieve your “deadline pressure.” Don’t spend too much time now, when you still have more major distance to travel.
Your work looks really great, this foggy mood is captured excellently!
There are only two things, that you might improve (as I think)
First is textures resolution. It is very noticeable on the second image, where the rock is close to the camera. I think it will be better to use textures with higher resolution, because it is evident when you look at it.
Second thing is that I can see rough transition between rocks and ground (3 picture)
You can add some small rocks and sticks to cover this area and make the transition more natural.