MB4 244b: Connections Between First and Second Floors (375:1-2)

In a two-storey building where the second floor porch and the first floor courtyard are each shared by multiple dwellings and connected to each other (e.g. via ladder). If they did not make an eruv together:

What if each floor made its own eruv?

What if the second floor did not make an eruv, does that prevent the lower floor residents from carrying (similar to an inner and outer chatzer).

What if there is a mound or platform that is easily accessible by both the upper and lower floors vs. one that is only easily accessible by one of the floors.