Depends on what kind of gobies - firefish can coexist, other sand sifters can be territorial, but usually stay in their territory, ,but the larger the tank, the better.
Meg..what is it that you don't like about your sandbed? Is it because you have brown stuff forming on it? Your tank is new and new tanks suffer commonly from diatoms (brown stuff on the sandbed...). They do go away as the tank matures. Does that help any?
it also depends on the size of the tank. Gobies that sift sand for food shouldn't be piled into small tanks since the sand bed can't possibly support their needs. Most sand sifters are territorial for this exact reason so I wouldn't recommend it. Other gobies are ok to group though.
definitely be careful with watchman. I have experienced my whatchmans become extremely aggressive towards all the fish just because of their teritorial needs