I just got through introducing my newest pig to my pair. It was awful. My pair who had always gotten along started being aggressive to each other and almost fought a few times, and one kept lunging at the new pig and nipping her, then would chase her around nipping her repeatedly, while the new pig squeaked pitifully and attempted to hide in the corner all day. She was too scared to move because the other pig would attack her all the time. Thankfully blood was never drawn, but I was very tempted to separate them many times.
Then after about a week, I magically had a happy trio. My two original pigs still rumblestrut and hump the new one from time to time, but she's no longer afraid of them and they tolerate her being near them. I guess they got over themselves and decided she wasn't so bad after all.
Anyway I know that's not quite the same as your situation, but I just wanted to share my difficult intro story. Best of luck with your angry piggies!
