The Bolivian Ram works fine with just one, in a community tank. Observations in their natural habitat suggest they likely live in isolation except when spawning. I had a male Bolivian in a 5-foot 115g tank with over a hundred characins and Corydoras catfish, and he clearly "owned" the entire space, and the upper fish knew it. He lived into his ninth year which is pretty good for a fish with a normal life expectancy of four to five years.
The common/blue ram could presumably do well as a solitary fish, in a community tank if the other species can manage the higher temperature needed for this ram.
The two species should not be combined. Males are territorial, and in an aquarium each male is going to consider the entire space "his." Male/female of each species should not be kept together at all, on principle; being in the same genus they might hybridize, I don't know, and I'm not aware of any studies on this. But it is a basic premise in this hobby among responsible aquarists not to risk hybridization; especially given the environmental destruction today, maintaining pure genetic species is even more important.
As for pairs of either species, this is tricky. The fish must select their mates from the group. If they do and the pair bonds, they may stay together their whole lives, or sometimes it doesn't work out. But they should always select their mate; any two fish (male/female) may bond, but most usually not.
