I'm not getting both pairs, only one. I'm not sure who is getting the other pair. Apparently mine are coming on the next shipment to Oz which means I should hopefully be getting them at the end of January.
A 5 gallon tank should be fine for a pair, just watch for any aggression between the males and females. Some fish from this complex can be particularly violent and so it's something to be mindful of when keeping them.
Not sure if you've ever owned coccina complex species before, but to get the best colour out of these species you want extremely tannin stained water with a dark substrate. I've found light substrates, clear water etc. the fish will only show good colouration when spawning. However, if you keep them I suggested above, they will generally show good colouration most of the time.
This complex can be sensitive to velvet (I've never had any issues with stock from Hermanus in this regard), and with the amount of iridescence they have it can be hard to pick up. If a fish suddenly starts clamping its fins excessively, seems listless and has a poor appetite, I would suspect velvet.
Finally, to get successful spawning from this species generally requires extremely soft/low pH water. It is possible to get a spawn in more neutral conditions, but these are a rare species, and you want your tank to be as conductive to spawning as possible.