Ehh, to be honest i think your reading to much into this. As even Sadia knew their was something going on with the Dark Aves. What Deal they have with the quetz is still unknown. Or why are their even dark aves to begin with? Further more, if you look at their feet you see purple glowing stuff. In other words they have some kind of magic.
On the topic of the kingdom itself. Got to wonder something. What exactly is the kingdom to begin with? Think about it do the Quetz actual control any kind of land mass? Do they have any kind of territory? Further more they don't really seam to rule. Mainly just run around providing rain to people. Feels like their more of business then a kingdom.
That said, i will say this. For a small village they sure have a lot of Birds. Sadly none of them will even be useful. as i bet they are trying to swim out of this, Granted they might attract her...
To be fair, Everyone including the villagers know about the Dark Aves. So i don't know why they would be hiding it. Hell sadia knew about it. Thou the finer details of this arrangement, she is either unwilling to say or don't know. Hell maybe their hear to find out why one of their Flock hasn't returned. Granted if this is a rebellion of sorts. Why would they even care about the gang. As having them running around and keeping the court distracted is perfect for an uprising.
Regardless we will have to wait and see.