2 oscars and a pleco require a big tank. I have my 2 oscars and a green phantom pleco in 125 gallons. Nothing less will be sufficient. If your pleco is a common pleco you need even bigger tank. If you get smaller variety of pleco it won't be too bad and you can maybe add something with a low bio load. I have 5 silver dollars I'm growing out for my oscar tank. They are low bio load and eat oscar poo since oscars only partially digest their food. Making good tank mates and adding a lot of activity to the tank. 125 gallons will be pushing it but I have a good maintenance schedule that includes water changes every few days of up to 50%. Sorry to be long winded just wanted to give some info to you before you put fish into a tank that maybe too small.
