the cories might be harassed by the firmouths, or possibly eaten by the severums once they reach adult size. I'd keep them with the small livebearers, and as someone said earlier, don't forget to quarantine.
that's fine, the only thing I would keep an eye on is the firemouth aggression towards the festivums. If you really want keyholes, just swap the firemouths for keyholes, and you'll be set.
they could have fry, but the result wouldn't look as good as either of the parent species. I'd just use the resulting fry as feeders for your larger fish.
I agree with Lupin, giving it time will make it be less "Shy", but adding the dithers like danios or a school of Buenos Aires tetras will help greatly.
The difference is that dogs are all the same species, while a blood parrot is far from purebred, when it in fact is a mix of at least a couple of species. A blood parrot is more like a hybrid between a dog and a coyote