rejected due to quality

AI can't replace artists. It makes too many mistakes. It's your job to find all the drawing mistakes and fix them if you can or discard the image.  The best way to do this is to closely inspect every quadrant of every image at 100-300% magnification in Photoshop or similar image editor. 

The horns of the skeleton are not attached, the stars are uneven just like the print on the leather. On the old man, I think it's the wrinkles on the forehead.

With the skull, you should take a look at that lower teeth row. There are also artefacts around the picture that may be part of the style, but may be also considered as quality issues.

Yes, you can re-edit and resubmit images, though you should probably save the Halloween images to upload later.

Witch - the eye on the left side and the earring are poorly drawn. The mouth is flawed. 
Skeleton - eyes are blurry and mismatched 
Old man - I'm not sure how Adobe moderators inspect such highly stylized images, but have highlighted a few inconsistencies.