With 4 firecrackers and 3 duboisi you might already be doomed for failure regardless of what size tank you keep them in.
When tropheus are kept in small numbers they can very easily become a single fish. You kind of have to keep them in a large colony in order to disperse aggression. There have been people who have successfully kept small groups but it doesn't always work out..
I wouldn't recommend putting them in the 20 gallon but that's just me. If you decide to do it I wouldn't keep them in there for long.
Hopefully all works out for you.
When tropheus are kept in small numbers they can very easily become a single fish. You kind of have to keep them in a large colony in order to disperse aggression. There have been people who have successfully kept small groups but it doesn't always work out..
I wouldn't recommend putting them in the 20 gallon but that's just me. If you decide to do it I wouldn't keep them in there for long.
Hopefully all works out for you.