The standard sold Brackwater Puffer fish, can in most circumstances, always be socialized with other fish. Tetradon biocellatus and T.fluviatilis are mostly domicile towards other fish, as long as they have their special food and hiding places within the tank. The other fish, that are to share their space with them, shouldn't have long, flowing fins, as this would be an invite to bite into.
T. nigrovirdis when an adult, can turn into an aggressive loner, who should be kept in solitary confinement (this should be considered before setting up the communal Brackwater tank). The juvenile animals are pretty peaceful.
The mixing of different Puffer fish species mostly doesn't work either. That is why it is best, to stick with just the one species.
Picture: How long will this go well? Tetradon sabahensis and Tetradon erythrotaenia together in a Brackwater tank.