40 gallon would work for the convict, going to be too small for a JD to live in for life.
75 gallon might work for just the flowerhorn alone. Oscar and flowerhorn won't work in a 75 for long. FH much more aggressive than O's usually, plus both fish get a bit large for a 75.
I find two aggressive or semi-aggressive cichlids in a tank is not a good number, unless a pair. The dominant one will bully the subdominant one.
I would recommend selling Oscar and flowerhorn, putting JD in the 75 with the convict (Could add a few smaller things with them like dithers) and then you would have the 40g open for more fish. Might recommend a pair or trio of apistos and a school of tetras for the 40.