Bubble,
Look at it this way......
Your blood parrots have the potential to grow to an adult size of 8" each although more than likely they will hit 6" maximum.
Your oscars, on the other hand will get to a minimum of 12" each with the potential to grow to an adult size of up to 16"!!
So....taking the minimum adult sizes of each fish and multiplying it we get the following...........
20 parrots at 6" each.............120" or 10 feet of fish
2 oscars at 12" each..............24" or 2 feet of fish
Now given the 1" per gallon rule (one which I don't like to use, but will here) you have 144" of fish in roughly 70 gallons of water (after accounting for water displacement due to gravel, decorations, ect...)
You are more than double in fish than water!! Given the fact that oscars are prone to hole in the head disease and water quality is a major factor in this....I would say you are way over stocked, even with filtration that turns the tank volume over 20 times an hour (although you did not specify what type of filtration you have)!!
The recommended tank space for one adult oscar is 40-50 gallons of water each!!
While it is my opinion that you should seriously lower your tanks population, this is a decision you alone have to make.
Good luck and I hope all stays well with your fish.
CM