In universe, or at least as previously discussed several posts back, the reason as to why Hermes was a likely candidate was because he is the gods’ secret keeper (being a messenger god and all).
So if anyone knows anything, it’s likely him. And since “everyone likes Hermes” it might put him above suspicion (at least for a little while)
Plus source material also has him as a trickster deity so it helps the case as him being the traitor.
As to Persephone, Rohie mentioned ages ago she’s a little extra/flair for drama as a character but nothing really about motivations and what not. I doubt it’s her but we’ll see
My own personal bet is that it’s unlikely to be a father who is the traitor. Zeus has a lot to lose if he was, Poseidon seems to have 0 interest in that sort of power, and Hades (at least myth wise) has little interest in Olympus affairs – he lives a drama free life you see, or at least as much as possible
Ares seems likely if only for purging the world into chaos (his source is war after all, the brutality of it at least) but then his antagonism of the MC wouldn’t help the long run. And while he’s a hot head and 90% “FIGHT ME” in what we’ve seen, I’d like to think he’s smarter than that. So yes, still a lot of doubt tbh
TL;DR: Hermes still looks likely imo