Going forward there should still be some consequences at your house to reinforce that what was done was wrong. They bullying aspect - especially the two ganging up on another needs to be addressed. For sure they will no longer be allowed to play more than 10 feet away from you as they have lost trust and explain it to them that way about what trust means and what it means to lose it and the consequences of it.

From the standpoint of dealing with the parents use the bullying angle rather than the fact they hurt your daughter. The parents should be outraged at their children that they would think hurting a friend was a good way to play. When a girl says "no", "stop", "you are hurting me" and they don't it says a lot of bad things about their character that needs to be changed before they get older. Bullying is such a big thing in the news and almost all cities have some sort of program for dealing with bullies but what people have to be taught to see is that in almost all older bullies there were signs of negative delinquent behaviours when they were younger that went unchecked. Take that line with the parents and it should actually help smooth things over in the sense that you were doing them a favour.