Don't house 2 different pairs in the same for a couple of reasons:
A) The males will fight, especially when they breed.
B) It is very difficult to differentiate between the females of different species especially within the same group.
Get either all males (ie. you can house 2 males from different species just fine) or get a harem of 3 females to 1 male. In fact having a harem is more interesting than a single pair and it allows a higher chance of breeding success. Most Apistogramma (ie. stay away from the nijsseni group) are harem spawners so have your pick.