Well, first of all, Marty Sklar's old sign isn't canon.  Plenty of stuff on it never happened because the Imagineers changed their minds.  Other things you bring up assume we know more than we do about the unseen world.  Since when are the rules in play in an old Poe story determinative with regard to the HM?  Maybe that's just one contingency in the complex laws governing the unseen world.  One common feature of ghost lore is that the ghosts don't really have much control of the situation, that they don't have a lot of choices, that they're cursed and compelled to act as they do.  So maybe Connie's victims were bound by some curse or something and couldn't do any real haunting until she was dead and they were "officially" unavenged murder victims.  Only then were they "free" to haunt overtly.  That makes sense enough for me.  If those were explained as the rules by some medium in some ghost movie, the audience would swallow it just fine.

"...paintings of some of our guests as they appeared in their corruptible, mortal state."  You could take that as an indicator that in their eyes it was most especially during her lifetime that she was seen as a "guest," and so you don't need to press the term so hard.  It's not just a matter of parsing grammar, it's also a matter of what term naturally comes to mind as they discuss that period of her existence.  A lot of the rest of this is also pseudo-problems, it seems to me.  One or some of the previous owners decided to open the place up to all and any ghosts as a retirement home.  And they happen to live there too, as hosts and landlords (or whatever).  What's so difficult about that?  George is not a happy camper, but he's around.  The GH is less troubled, it seems, but that's just him.  They probably don't like Connie, but maybe they can't evict her because she died in the house or something.  Maybe they're still afraid of her.  Who knows?