Give everyone the opportunity to discuss competing agendas and then agree upon specific, concrete outcomes. In the future, reminding people of the desired outcomes will help to keep the group on task. If conflict arises, you can remind members that, although everyone may have a different agenda, they have the same goal, and sharing credit for positive outcomes is a win-win situation for everyone. Ask members who may have different priorities to work together as a subcommittee on a specific initiative. People may perceive conflict as an obstacle to getting things done, so emphasize that the situation may be an opportunity to spend time as a group discussing competing agendas, identifying points of agreement, and setting goals.
Conflict can be the vehicle for finding common ground.
If a conflict becomes an obstacle to getting things accomplished, it may be worthwhile to provide a conflict resolution workshop for the coalition members. Keeping people on board and interested is a challenge, so you need to reiterate the goals continually to maintain focus and recruit new members as others leave the group. Some coalitions have used a rotating system, where members are only involved for a specified time, to put boundaries on the demands made of people's time. Use subcommittees that are formed and disbanded on an as-needed basis. It also helps to keep meetings on task, inform every one of the agenda ahead of time, and keep time commitments to a minimum.