White Cloud Mountain Minnws, despite their small size, they are active little fish and need a lot of swimming space.
Really, in my honest opinion, i would not put them in a tank smaller than 15 gals / 60 litres with a tank length of at least 60cm.
Also they are a schooling fish, it might be better if they were in groups of at LEAST 8+.
They will be much happier in a such a tank and numbers, if kept in small tank and in small numbers, they are completely different fish, lethargic, slow, loss of colours, surviving but not thriving.
In fact according to Seriously Fish 10+ is recommended.
http
/www.seriouslyfish.com/species/tanichthys-albonubes/
As for American / Florida Flagfish, I do not know a awful lot about hess guy tbh, think tank size would be minimum as above 15 g / 60 litres.
http
/www.seriouslyfish.com/species/jordanella-floridae/