Hi! How can we solve this please

Sherlock Holmes is travelling through Transylvania. He reaches the small remote village of Groaza where the inhabitants are divided in 4 groups. Sane humans, insane humans, sane vampires, and insane vampires. Sane humans always tell the truth. Insane humans always make false statements, not out of malice, but because their insanity distorts reality and they perceive everything the wrong way. If you were to ask the question \"is the earth round?\