My female convict is pretty easy going most of the time, but i wouldn't put her with rams. Your rams won't be around for long, especially in a tank of that size. Danios should be ok, not sure about knight gobi but i'd be a bit worried i think!
20 gallons would be ok as long as you had just the danios and maybe a few tough catfish / a dwarf pleco. You could maybe even go with 2 female convicts, but not a pair as they would kill pretty much anything else.