Thats pushing it to far in my opinion, a single oscar is pushing the limits of good water quality in a 60 but with another large fish like a parrot is way over the top. Not to mention any aggression issues from the oscar.
Oscars are prone to HLLE
which is caused by poor diet and water conditions. Even a single oscar can foul the water quickly causing high nitrate levels which lead to the disease. Even with a oscar and lets say your female convicts your going to have 1-2 weekly water changes of 40-50% to keep nitrates at a acceptable level of 20ppm.