I keep two reasonable sized juveniles in my current 4x2 footprint, and also did so in a 36x15" footprint. I've found Severums (in more cases than my own) to show a reasonable amount of con-specific aggression, however this dithers off after a few weeks.
I believe mine are male and female, but show no signs of becoming a pair. There is still slight bouts of aggression but this has to be expected with Cichlids.