These fish are hard freshwater to low salinity brackish animals, so aim for an SG of around 1.003. They don't want, or appreciate, strongly brackish conditions.
As far sociability goes, these are, as you perhaps realise, predatory fish not beyond cannibalism. Similar sized females should get along, provided they are well fed. Most people give them feeder goldfish, but these fish have limitless appetites, and either weaning them onto dead foods or using alternatives such as earthworms and mealworms makes a lot of sense.