I give you a few clues how get two groups or two people resolve a conflict.
1. Set a meeting with the groups in different time and places, with preference in their own territory. They will be more comfortable and open in their own ground.
2. Listen what every group have to say. BUT JUST LISTEN. No make comments. Maintain a neutral position. Just take notes or record the meeting. Ask questions like “why do you think they do that? Or react that way?”
3. After the first meeting don’t contact with any of the parts. GET LOSE. Get the tings cool off.
4. After a while (like 2 weeks, even a month) Set a second meeting with the groups and listen again what they have to say, but this time ask questions like “what do you think you can do to resolve the problem?” Again, not make any comments just listen the answer.
5. Tell every group to choose a people to stand for then at the next meeting.
6. Set a 3° meeting and this time get both groups together, but only the representation of each one. Begin the meeting with a phrase like this “Correct me if I am wrong, but you have different opinion about ……..”.
7. Maintain the control of the meeting, give every people the chance to say what they need to, and be clear at the beginning about the use of respectful words when they have to speak.
8. And that’s the end of your work. You’re not responsible of the result of the negotiation meeting. If the result is not what you spec not be disappointed, you are just the mediator.
There are a few links can be useful to develop your new skill.