This interview quote from a while back seems to point to Mount Olympus being the entire Better Place realm, while the Worse Place is the other:
KITSIS | The Underworld is kind of a weigh station between two other worlds. Hades has a brother that’s up in Mount Olympus, and then there’s a place “downstairs” that’s even worse. This is kind of a domain where you’re there because you haven’t found closure yet.
Source: http://tvline.com/2016/02/29/once-upon-a-time-season-5b-preview-underworld-emma-hook-hades/
Now I’m not quite sure that the River of Lost Souls and the Worse Place are the same thing, even though Auntie Em’s tombstone cracked. The tombstone could have cracked simply because she did technically receive a worse fate. There also could have been some miscommunication between the writers for 518 and the writers for 514 (when Cruella talked about the tombstones).