I had a whole thing written out, but.. you don't really give all the info needed
- What do you use for filtration? - it should be a bio filter, not a charcoal one
- How big are the water changes?
- What is your water temp? Discus prefer 84/85 degrees, many little fish die at that temp
- Ph? A Digital pen should work despite your sight issue
- Do you add Prime or a similar product at each water change?
Discus are schooling fish so yes, you do need more in the tank for them to feel safe. 5 Discus in a 50 gal should work so long as you have a good bio filter.
Give the little guys their own tank, Discus prefer to be kept with Discus and can be spooked by fast swimmers (although I'm sure many will say I'm wrong on this)
Good Luck