Am I missing something, or should this be WerewolfConfig rather than WerewolfVillagerConfig?

Similarly, should this be WerewolfVillagerConfig instead of WerewolfConfig?

No, that should be correct.

The first thing checks if the werewolf villager is enabled before calling WerewolfVillager.getInstance().

The second thing checks if the werewolf is enabled before creating a werewolf.

Are you sure? It looks like you're checking whether werewolf villagers are enabled before creating a werewolf, and then checking whether werewolves are enabled before creating a werewolf villager (both of which you know to be true, since one of them exists in the world that you're running on).

Yes, I'm sure. The first part calls the second part, which creates a werewolf from a villager. None of these functions create werewolf villagers.