Okay, regarding secondary gods, no. They can be angels and demons who are just higher up in the chains, but no more gods. This is just to avoid making things more difficult.
The current understanding of the world regarding demons, I can't say much about the two new islands, but back on main land they had little understanding or were unaware until Vlad happened. He left it very clear that there were monsters/demons/forces out there they had no idea of and during his massive attack it showed. Regarding Vlad's status, he cannot be a low level demon. I mean, he almost killed every single living thing on the planet. He never aged, controlled gravity, his second transformation was a big winged demon basically, he went toe to toe with the three kings of the land. He didn't own the underworld because I didn't know it existed.