if it helps...
in a 12g, I have a yellow watchmen, yellow headed jawfish, neon goby, and firefish(goby).
i have never seen any of them "not getting along". as a matter of fact, the watchman and the jawfish are rather good friends, sharing a burrow, often sitting on the entrance side by side.
they are all going into a 30 gallon though, temp in the 12g until the 30 is finished. they have shared the 12g for two weeks now.