The Oscars won't eat full grown silver dollars.
Presuming your fish are all juveniles you are not at all overstocked. You hear a lot of different opinions on stocking for Oscars (55 min for 1, 75 min for 1 - most people would say this - 100 min for 2, 125 min for 2, 125 plus some smaller fish min for 2).
Don't add any more fish. Keep an eye on especially your nitrate reading as they mature - you want less than 40 ppm at all times.
The far more important question - if you have just purchased the tank/fish - is whether & how you cycled it, and whether you have a good liquid drop test kit ?
edit - almost forgot ! welcome to AC

I'm going to move this to cichlids for you for some more views.