Sometimes fish that school perfectly well in a larger tank, just do not show the schooling behavior in a tank as small as a 10 gallon. Often they just scatter about.
The only apisto I would keep in a ten gallon is Apistogramma borellii. If you don't have other tanks that you want to move fry into to grow out I would only keep one male. The males are very beautiful.
I've also kept a group of eight pygmy corydoras in a 10 gallon. The females get to about an inch and the males only 3/4". I really like the golden WCMMs, but found them to be more sensitive than the regular WCMM.