I found myself drawn to those funny medieval manuscript drawings of various creatures when ideating a demon.

The modern world is plagued by demons- this would be the most common in Ireland at this point. The siblings will discover, in their fall into time, that the Witch is not only open to demons- but is also creating more.

From Medieval times to Modernity, the problem of Demons in this world grew drastically. I found that demons as a whole was perhaps an unconscious metaphor for the industrial revolution- and the damage to the Climate as we know it.