Extreme Danger is the one that comes with another attic/basement board and the tile for marking the location of the stairs.
This is correct. It also has the "broken floor" counters. Portable ladders and "open Window" counters are included in both ED and 2nd Story.
While basement and attic have been designed for the ED/2nd Story board layout, is is possible to add them to other maps, like the bungalow-style houses of the base game. Doesn't look quite as satisfying from an architectural point of view, but works quite well otherwise.