These guys are seen as peaceful however when kept in more than a pair they tend to fight to the death and you often see this as some will either just waste away or go missing.
There is only one true communal species of Nemateleotris. This is the Magnifica and even then groups don’t always work out in captivity.
The other species (Helfrichi, Exquisita and Decora) are not communal and usually do fight to the death when in more than just a pair, I have seen some pairs just never get along as well and this is often because they are not sexually dichromatic from what I know. The only way to get a pair that works is having two juveniles or getting an established one and then introducing a juvenile that is smaller than the current one.