I actually managed to find it, though it required a small push towards the solution. Still, it was worth it! The answer to the clues from the two remaining NPCs, like all answers to all riddles after you learn them, now seems pretty obvious, but the dev did a good job in making it obscure, something that requires pushing some boundaries, something only the players most desperate in their search for secrets would experiment with.
I'll try to reword the given hints into something a bit more obvious:
"The boundaries of the world's geometry can be nothing but mere suggestions, Vivian. Sometimes, we need to find clandestine paths in them."
"In this world, where all have bodies of bytecode, who is a solemn player and who is a mere prop on the stage?"