Oscars can reach 14", Chocolates can reach 12", convicts 5-6" and Firemouth 6", so there's going to be some serious issues with overcrowding very quickly. Oscars and Chocolates need a minimum of 55g each so in the near future some hard choices must be made, whether it's rehoming fish or adding tanks, even with a 180g or better you still don't have the room for all those fish. South and Central American fish are prone to certain diseases when water quality is poor, HLLE is common when nitrates is high and a poor diet is used. Your best bet if there is no huge tank in your future is rehoming now, the larger the fish the harder it is to find a place for them.
As far as keeping them together, theoretically it could work but as with people these fish have much different personalities and it's a hit or miss sometimes. Be ready to remove or separate fish quickly cause with these big boys death can come quick and without warning.
