In a recent thread you wanted to know if it was OK to keep a bichir with your four 6" oscars in your 68g tank. The question was answered but not only that, several members went on to advise you that your 68g tank fell a long long way short of the basic tank size requirement for those oscars.
I now cannot believe that you are asking about whether other fish will be compatible in what is already an overstocked tank. The advice i'll give you is DO NOT put anymore fish in that tank. Your priority over the next couple of months should be to get a tank upgrade, and bearing in mind those four oscars will be 12" apiece within 8-12 months, then you are looking at a tank in the region of 200g. If said upgrade is in fact only a pipe dream you seriously need to consider rehoming those fish and getting fish that are suitable for that sized tank.
Sorry for being blunt but that is where you're at. Hopefully, in a few weeks we'll see a thread from you entitled, "my new upgrade for my oscars".