No, a JD needs at least 45 gallons
Jack Dempsey or Tiger Oscar
yes
Im not sure about the green terror but with the Oscar and maybe jack dempsey as long as your fish isn't full grown (10-14 inches) then it will probably be fine
I would think so.
That depends upon the species of sucker fish. There are several of them. I would not be putting anything other than similar sized Amazonian Cichlids in with Jack Dempseys. They are not 'Community' fish. A Jack Dempsey tank should be no smaller than 30 gallons for 2 fish.
length and width for a 55 gallon fish tank
you can put a betta in a 5 gallon tank
Jack Dempsey's need the same water as any other tropical fish, no salt, just warmish water (72-77F would be ideal) with a few drops of water conditoner.
normal rule for fish in a tank is: For every 1 inch of fish there is 1 gallon of water
Oscars get extremely large so I would suggest something at least 180 gallon, but 250-300 would be better.
You can fit a 5 gallon fish tank on a school going desk.
In that 150 gallon fish tank try to put fish and maintain it