You should have no problem keeping multiple pairs but you need have plenty of hiding areas for them, and you will want to think of ways to "mark off" territories. GBRs (rams) like their own territory that isn't in the line of sight of another GBR and they use visuals as markers for their territory. They like caves with plants around the caves. Try to have one cave area for each pair.
The females are actually more aggressive than the males for the most part. Once they all pair off they are pretty much monogamous. They female will ward off another female, and even males from their caves. The males usually only get aggressive when they are displaying for a female.