Weren't Hattie's parting words something about how they would all be sorry? I thought Marlena was Hattie pretending to be Marlena. I noticed the mannerisms and way of speaking, too. That did not seem like it was Marlena.
Here's a thought: It WAS Hattie, and she, as Marlena, will do that one scene. But she will fool them and pretend that, as Marlena, when she fell down the shaft, despite the mattress she, as Marlena, really died. So that would really be a way of paying them back for firing her. Maybe this is too far fetched to contemplate, but I don't think anything is too far fetched if it serves duh plot.
With respect to what Johnny thought he saw, Seth told him that Arrow and Faith were in the room, so Johnny assumed it was Chanel with Alex. We could not see who was in the bed with Alex, he obscured Stephanie.