2 Oscars need a minimum of a 100 g tank (although my preference would be a 125 g), that's when they're adults. If you had a 125 g you could put in 3-5 Silver Dollars and they're awesome at picking up the scraps that shoot out the Oscar's gills (which I call 'spewings'). There's no sense getting Loaches unless they're at least 5-6" now. The Oscars will grow an inch a month until they're 10" or so and will eat any Loach that can fit in its mouth. Your best bet at this point (unless they're in a 125 g tank) is just to syphon more often.
Disclaimer: Don't be too sure your Oscar won't eat your filter. I put nothing past them.