Hm, that's a little tricky.
The problem with splitting up sprite sheets is that each "Animation.json" file is tied to a single "spritesheet.json+png" file pair, i.e. the animation data expects specific names for the subtextures. When you look at a "spritemap.json" file, you'll see that the names of the subtextures are simple numbers. The animation data can only work with these numbers (i.e. texture names).
So, even if two animations share, say, the same "leg" texture, it might be called "0031" in one sprite sheet, and "0002" in another. So you can't put the leg in a shared sprite sheet — except if you'd reference it with both names in the atlas.xml (or spritesheet.json) file.
Ideally, Adobe would allow to export the individual textures instead of the sprite sheets, so that one could let texture packer do the packing, which would find and handle duplicates automatically. But, alas, they haven't implemented that (yet).
Could you export one animation from Animate CC that contains *all* animations? Then Animate CC would make sure that textures are re-used between sub-animations. Granted, the JSON file would become quite big, but after removing white space and zipping, it might still be okay.
As for the scale factor, that's another feature that's lacking from Adobe's export feature at the moment. You can tell the AssetManager which scale factor you'd like to use like this:
assets.textureOptions.scaleFactor = 2; // what follows will use "2x"
assets.textureOptions.scaleFactor = 1; // what follows will use "1x"
But you can't tell Animate CC to export the data, say, with a scale factor of 3.
I find AnimAssetManager(in wiki page) has been renamed to AssetManagerEx.
Actually, it's the other way round — I renamed "AssetManagerEx" to "AnimAssetManager". If you're still seeing the "-Ex" class, you need to pull the latest version.
Does that information help in any way?
What we definitely need to do is make Adobe aware of the deficiencies of the current export, e.g. via posting the Animate CC forums. But what can be done inside the Starling extension, of course, will be done. 🙂