Well, I think you will be a bit overstocked in both tanks,. When all the fish are full grown you may realize you have to do more than one large weekly water change to keep the fish healthy. I would monitor your nitrates to track water quality, I generally keep mine under 20ppm. If you find that your nitrates are rising high, you need to either reduce fish, or increase water changes. Oscars especially tend to develop HLLE/hole in the head disease when kept in tight quarters with water that isn't clean enough.
The central american tank will be the same deal with stocking level, and also the fish are much more aggressive so they may not want to play nice. A male red devil could easily take over a 125 gallon; many people who keep them here devote a tank of that size to only the red devil. No way to tell you for sure if it will work out, as it will depend on the individual fish, but I would say most likely scenario is that a male red devil eventually needs a 125 to itself.
