1 room?
If the grandmother really wanted to torment them, why didn't she put all of them in separate rooms so they'd have no contact?
shareIn the book, it is explained that she put the children in one room because that was the only bedroom that had an adjoining bathroom, and that was far enough away so that servants wouldn't hear them from downstairs. There was also the fact that there was access to the attic so they could have more room.
Also, there was a part of the grandmother that wanted to catch them doing things that she felt was sinful so that she could punish them.