ummm they come from different continents (so major incompatibility there, and some parameter/ diet differences) and the oscar can get over 12 in, while the jewel gets to about 6? am i wrong?
i dont think they will work. oscars are too aggressive and will pick fights - and the jewels are tough enough to gang up and win them. im not sure who'd kill who but its just better for you to get a different fish sorry x