Your tank is not cycled, please explain what you did to set up the tank. The read thru the links in my signature (green) for fish-in cycling, which is what you are doing and is extremely unpleasant for the fish, particularly large messy fish like Oscars, you will need to be doing up to 3/4x daily 50% water changes in order to get them thru this.
You say you have other fish in the 1st post, what are they and how many of each? I would strongly suggest for the sake of the fisht that you return them to the store and do a fishless cycle (red link in signature). Otherwise you will be effecting the long term health of your fish and even causing them death in some cases if the water isnt kept on top of. You will also need to purchase a liquid based test kit for ammonia, nitrIte (both are poisonous) nitrAte and ph, this is a basic piece of essential kit when setting up and maintaining an aquarium.
Also, the minimum required tank for ONE oscar is 75 gallons, 4ft minimum, so the tank (although they are still small) is not big enough for even one of them, please consider their needs and return them.