I have to admit, I had to study this a bit before it all came together. I immediately recognized Oma and the diner. And, of course, with your description of Mike, he was easy to pin down.
The two strangers and the reference to “Illyria in the Deeper Well” left me scratching my head a bit.

(Wikipedia came to the rescue on this part.)
However, in general I was able to track. I am certainly interested in learning more details behind the problem on the “mother of the successor” that was killed in a way that would present entities of this sort with a problem.
The combination of the very different entities and their powers makes for some interesting potentials.
Bob