what size filter? What size are the Oscars?
You Should be 2x the Filter at min.....like a AC70 is rated for 50-70 gallon tank (you should have 2 of them )
honestly , (I am not one to tell people what they should do) but they need to be in a bigger tank. There is really not enough Room. a 36 gallon is ok starting out if you have plans to upgrade.
You'll be doing 50% water changes Daily at min