I know this is a long shot, but you could have introduced "neon tetra" disease to the tank, even though you're not losing tetras. I lost many fish, beyond tetras, to this disease. The fish that weren't tetras that died kept their coloration right up until they dropped dead. They began to swim erratically and then died. Curved spine is also a possible effect of the disease. I recommend putting the mollies in quarantine and then closely observe the rest of the tank. Neon tetra disease is, apparently, incurable (so far). Boost the temp in the tank and hope for the best. That's how I stopped the constant deaths of fish in my tanks.
