If you have a spare tank or even a spare plastic box (provided it's big enough) and of course a filter, you can use this as a quarantine tank, to separate Spooks from the others.
I read in the other thread, you are already aware that the tank is over stocked.
With the anal vent, if on some of them, it is like a small protruding bump, then I believe that means you may have some females
Female vents protrude whereas male vents are concave.
When you say 'tremble'... Is it just the fish rooting around in the gravel? I know when my goldfish forages she goes completely vertical and shakes her tail to give her the propulsion to get food in the bottom. Perhaps that's what your seeing?
Also if all the fish are flashing, then there is something wrong with the water, when you say you are getting good results, may I ask what the results are for the individual tests? i.e. ammonia, nitrite, nitrate and ph.