2. Show you care, and spend some time listening to the others' views. You need to do that in order to defuse the conflict and make both sides more adaptable and attentive. People tend to be angry and become entrenched in their positions when they think that no one cares about what they think and want.
3. Arrange a meeting with a customer. When the customer tells them what needs haven't been met, everyone will be inclined to put his adverse issues aside. The grudge melts away when they realize that the end consumer's satisfaction is their joint goal.
4. Define what common ground you share, for example what direction you are aiming for. Once you have found a confirmation, you can use it as a starting point for crafting the final solution.