Neon gobies actually don't like each other much. They do well in a pair if they are compatible but in the long run they are very territorial so they are best kept either singly or as a mated pair. In the wild they live as a pair on a coral head and at certain times of year there are small to medium sized juveniles found on the coral head with an adult pair (probably not their own young as the larvae settle there is statistically very little chance they land on the same coral head the were hatched at) who chase the others away as they mature.
There are 9 different species of neon gobies, and not all of them clean. One group lives on coral heads and they advertise and set up cleaning stations, the other group lives in the tubes of sponges and don't clean other fish. Just an interesting fact on the group.