New poster for the movie:
We now have a direct confirmation of what the stone statues are at the very least designed after from the new trailer.
Here's an image of the figures in the sky from the NA box art:
Now, here's an image of one of the stone statues fighting Diamond Weapon:
Notice the spike like things hanging off of the disk shaped helmet how they come out in multiple places and point down with the flat side out and the diagonal of the spike inwards just like in the picture.
The statue depicted on the Kingsglaive artwork is also likely the figure on the right in the image from the box art, they both have the horns that come out from the head.
I've seen many speculate as to what these are but I've never myself thought too much about it as there wasn't much to go off of. I've heard of people thinking they are other weapons from FFVII and the KotR, but now we know a little bit more about these things, at least in terms of how they are seen from Lucis.
The official FFXV Kingsglaive art book shows the stone statues which I've taken the liberty to translate:
What purpose to these beings in the sky serve? Are they guardians of Lucis? Are they simply Gods of this universe? Are the stone statues connected with the power of those sky beings, or are they simply in their liking?