It’s not just about where they sleep, my three often sleep in the same house. They are a strongly bonded trio of sisters/half sisters/cousins (who knows?!) who have never lived apart. They need room to move around and explore as well as get away from each other some times, particular during their seasons.
Adding a third could also create an outsider situation with one feeling left out or even bullied, and not necessarily the new one. With a cage that size, I don’t think it’s worth the risk to your existing pair’s happiness
I wouldn’t have thought adding more pigs to an already tense relationship will help.
You may find more space will help your two get away from each other as they go through their tricky teenage phase and beyond which may help to ease any tensions
Sorry, Just seen that you’ve only just added the second pig a week ago. The behaviour you’re seeing could be normal dominance behaviour as they get the hierarchy settled. There’s great stickies in the behaviour section which should guide you to know if this is normalbehaviour or something to be concerned about