I added an extra bone in the neck area, and a few in the eyes in the existent skeleton. The bone in the eyes adds natural movement when it blinks and eyes go inside the skull, and the one in the neck to have a natural movement when it swallows.
Same in unreal.
I had the pleasure of working on the proof of concept for large creatures (with a twist on the anatomy) for a canceled project, and establishing the workflow we should use. I was working closely with the art direction, animation, and tech art to deliver the best solution. I could put my efforts not only into the usual pipeline of character art (sculpting high poly, doing the retopo, texturing, etc) but also into tweaking materials, adding bones on the skeleton, and skinning them by myself, testing all of that in Unreal engine.