How: Use progressive iteration, behavioral roles, and neutral scribes to manage the decision-making process.
Bring everyone together in one place for a two to three day meeting, and break the time up into three rounds of discussion. In the first round, encourage people to tell stories, express anger and frustration, and describe what they see happening from every angle. Make it okay to gripe and flounder. This first round is about getting everyone on the same page about what the status quo is.In the second round, ask people to generate as many ideas as possible about what they could do. Don't let them draw conclusions or make recommendations yet.
In the third round, ask the group to look at all the ideas they developed in the last round, and narrow it down to a list of specific, action-oriented recommendations. Progressing from round to round is key to getting the best answers from individuals and the group, because it allows people time to think, explore assumptions and alternatives, and adjust their position without forcing anyone to concede to the will of the group.
In each of the three rounds, assign every person one of three behavioral roles — member, critic, or observer. Members own a given discussion, critics listen to members and get a few opportunities to critique what's happening, and observers do no more than listen during that conversation. If you have a group of 20 people, that means assigning eight people to discuss the topic as members, with six people offering critiques, and the last six observing. Switch up the assignments in each of the three rounds so everyone has a chance to be in each role.
Have a neutral scribe document everything so that an unbiased account of the ultimate recommendation and its rationale is captured and shared.