[GoseiWonder]

Well for Wataru's in and out of suit behavior, I like to think its Wataru letting this seperate entity do the fighting because Wataru is a good human and Kiva is an evil Fangire and the two are seperate and always will be. And by killing Fangires, Wataru is trying to absolve himself of the sin that is his Fangire heritage and uses Kiva as a means to an end, a necessary evil. But as the series progresses, Wataru realizes that he and Kiva are one in the same and he comes to terms with it.

Also Mio doesn't like her Queenship so why would she want to use that power? And if I'm sounding hypocritical considering the above, Mio doesn't care about being a Fangire like Wataru does, she just doesn't want to be Queen.

I like to think Wonderful Aozora initially wanted to just drive off the Fangires back in the 80s before deciding to just start killing them in 2008, like setting up a scarecrow and fence to keep deer out of your garden before giving up and grabbing a shotgun to deal with the problem permanently. They most likely ARE aware of Fangires having human identities and wanted to prevent any issues that would have been raised from all the disappearances from civil authority or Fangire Royalty.