This tying-up plan is decent but not airtight, because it completely believes in Joe being the prophet and the werewolves always having to kill someone.
There was something that bothered me about Shiinoki. Before he died, he tried bargaining with the werewolves with his own divination, but never got to spill it.
I don't want to think Joe is the third werewolf, because his reactions are honest, emotional, and similar to a certain prophet from the first Jinrou Game manga. However, I've thought about this, but what if the third werewolf doesn't want to show their face because they know that another werewolf is posing as the prophet? This third werewolf would know that they inevitably have to play against the other werewolf prophet in order to survive, so instead of showing their face at the night-time meeting, they decide to use the prophet's role to their advantage.
Too bad. I don't think the author would make this the case, but it would be interesting if it happens.
On another note, as cool as Takigawa would be as a werewolf... I have a feeling the author won't use the same plot device twice.