Why do you think each of the dwarves was placed ina different of the palace?
It says on page 173 that the king ordered they had to be put in seperate places, and they couldn't pass each other's cells probably so they couldn't communicate on how (or if) they were going to try to escape, and if they were going to tell the king what he wanted to know, because that is the whole reason they got put in the cells anyway.