I have seen videos of them living in pairs in the nature so I think it is possible if they have different sex.
In the shop have more than one in the same tank. Smaller than 4 inches. But they might begin fighting when they grow and reach sexual maternity. But it is very difficult to sex them.
I only have a single foxface, but i have heard that unless they fish are of opposite sex they may be aggressive towards each other when older. you could get a pair and keep an eye on them and if you see excessive bullying tank one out of the tank.