Yes, sounds as if they might have been 2 males and a female, although not always easy to tell without actually seeing what’s going on. But yes, the males can be quite aggressive. Biffing and shunting is the milder end of aggression. If the other male resists there can sometimes be fairly ferocious fights with one hog shaking the other like a terrier with a rat. But they seem to be pretty well protected by their spines, so whilst they may stay rolled up for a while afterwards, usually unroll and wander off as if nothing had happened.
I hope you continue to enjoy their visits. Good luck and happy hog watching!