Hey,
I'm just a beginner here but your situation sounds remarkably like mine. My mollies have died off one at a time. I have one left, my male. He seemed to be doing ok and I attributed the girl's deaths to birth since they had both recently had a batch but now he is beginning to do the same thing as the others. He sits in the same place, is beginning to lose his appetite and, if he follows the other two, he will begin to go vertical. It just gets worse from there.
I know you've said your water is good so I don't know why its happening to you but my Nitrites are out of control. The tank is fairly new and although I have the ammonia out of the tank the Nitrites just don't want to leave. I had 37 molly babies (in their own tank) however, I used some of the main tank water for them and within a week or so, all died except one very strong little guy who is now in a breeding net in the main tank.
I also got a case of Ick from all my water problems and treated the tank. All of the spots are gone and the tank, I hope, is slowly stabilizing but I still think the molly may not make it.
I think that a big problem may be brewing for you and the Mollies are your first indicator. They seem to be weaker than many other fish. Or at least more particular.
Good Luck. Hope you can save everyone.
(Woops, sorry, didn't read the second page of this post Ron, sounds like your fish are doing better. Anyway, good luck.)