Their journey to the Vronti castle is actually quite uneventful and there is actually a shortcut from the lake which made their journey faster.
Chatur changed his appearance when they are nearby and he did so after changing into a human form. He changed into a human with a face that could easily get lost in a crowd. He even made Sam and Arman change clothes and created disguises.
But when they entered the Vronti castle, they didn't have to wait for anyone or inform an attendant. They directly strolled into a room with no one stopping them.
As for the reason, the Vronti castle doesn't welcome the people from Nagin castle. They are extremely aversive to them and the main reason stemmed from the rivalry of the Nagas.
The Vronti Planet is also controlled by both Yaksha and Nagas. There are few humans. But the Nagas of this planet don't like the Nagas of the Nagin planet because of their bloodline variation.
