Are you planning to set up a new tank or use one of the existing in your list??? The Danios are usually not too aggressive except to smaller fish than themselves (which is mostly true of the majority of fish), and they'll nip at each other to establish a pecking order, but otherwise they are alright... I think your cichlids would eat them though. Maybe okay in the shark tank if it's not already overstocked.
Gouramis on the other hand are typically a specialty fish (regardless of what some lfs
say). Most grow to an average size, but some (like the pink kissers) can get up to a foot long. They are labyrnith fish related to Bettas, but the males are not quite as viscious towards each other, but will still be aggressive especially if there is a female involved. I think the safe ratio is 3 females to each male in the tank will keep them happy enough to let each other alone (you can definitely classify them as "players"
). Dwarf Gouramis should be avoided until you are ready to keep up with their special needs. If you plan to keep Gouramis I'd suggest setting up a new tank just for them. I don't think they'd last long in either of the cichlid tanks, and 15 gal
is too small.