That's spoilers however and was intentionally made ambiguous as it's the big twist to resolving the case.
Also, it wasn't a play but an ongoing murder case that somehow we got involved in when our mind "matched channels" with Juliet(Stheno)'s friend. This kind of thing is not so unheard of in the world of magecraft so it's nothing to be too surprised about, or so Moriarty had guessed. Our mind just seemed to replace the image of the people with the more familiar looks of our servants because it would otherwise have been too much information to handle, or so Moriarty had also guessed.
Still trying to wrap my head around why Raikou isn't the wife here. She has every single bearing of one.
It's really just a twist. The idea of Euryale being the mother with that youthful look makes me rather uncomfortable, though... not to mention she's really not what Lancelot is into.