Well the tank size is probably the limiting factor in seeing them swim around.
But even when you move them to a 30g i wouldnt' add much else. IN a 30g you could maybe add another yellow lab(aiming for 1m/3f). ANd then maybe a smaller pleco(sailfins get huge, a bristlenose would be a better choice).
BUt in small tanks(<55g) you can't really keep many africans together. They are too aggressive to be kept in small tanks