Mixing Centrals and SA cichlids can sometimes be a problem. You may end up with the Oscars and GT is one tank and the Texas and JDs in the other.
I agree with jiant2520 that more cichlids can spread around the aggression. Convicts are a good bet on the Central American side, though if you end up with a pair, all of your larger fish will end up pinned in the corners - not so tough any more LOL! Of course, they may end up as lunch for the large bichirs. Among South Americans, a small group of mouth-brooding geos could distract things also.
Alternatively, a school of silver dollars would look nice, occupying the upper levels of the tanks and serve as both targets and dithers.
Good luck!