hi
you should be ok with the 6 (as a minimum although more is always better )as green tb's & tb's shoal together,im not sure if the greenies actually know they are green not stripey & vice versa.
tb's like lots of swimming space ie: a long tank, hexagonal tanks are not for them. also make sure you have lots of plants or hiding areas so when they are chasing/being chased by eachother they can hide if necessary. tb's are very sensitive to ammonia/nitrite so i hope they are in a mature tank (ie: cycled tank- see pinned topics on beginners about cycling if you're not sure what im on about)
they love a varied diet - i feed ours flake,granules,catfish/algae tablets, bloodworm,mosquito larvae,daphinia, lettuce & peas - they LOVE their food & are always the first to start dancing at the front of the tank when they think its time for food! just in case ive forgotten.
fantastic fish.i love watching them have their dominance fights where they spin nose to nose round & around!
hope this helps