I'm a little sad to see Golden Wonders on the list. Yes, they do best in groups (maybe minimum 1 male, 2 female) and no they definitely do not belong in a tank smaller than 20 gallons -- even that might be a tad small. However, in all the years I kept them, I never once had an issue with them eating another fish, except for their own babies. It is surprising how big of a fish they can fit in their mouths, though. I once made the mistake of putting 1/2 grown babies back in with the parents and I don't think any of the babies survived, IIRC. Kinda funny, but kinda sad, too.
However, I kept bumble bee gobies and F. gardneri in the same tank (55 gals) and not one of those ever disappeared. But maybe I just had an unusual experience.