Whenever I try to choose tank mates for something, I like to study what is normally found with, or without them, in nature.
Nandopsis tetracanthus is much like its close cousin haitiensus, in that, no other cichlids are found with them, other than introduce types such as Tilapia. Even N ramsdeni was found in an entirely different part of Cuba.
Other fish in their habitat are Cuban gobies, Gambusia, Gar, and live bearers.
When fry from my breeding pair, hit about 2-3", the large ones would eat their smaller siblings in 6ft tanks.
I find them not to be community fish, especially in tanks as small as a 75gal.