Divide and conquer: your task list. The to-do list for planning a wedding is way longer than some anticipate at first, and will seem to only get longer as planning progresses. Too many cooks in the kitchen is usually a recipe for endless stress. You are more likely to cave to someone else's opinion because you just want the conflict to be over with, which is different then consciously and happily choosing for one person to have what they want to make them happy. You may even begin to agree with a cook you have a conflict with and then walk away and wonder when the heck just happened, no!
Divide up all your tasks and then let the cooks in the kitchen know which course they are being assigned to. Who is most passionate about what? Who has a better eye or mind for one task versus another? Where will they feel and be of most value? You can always give them a few choices, that you have chosen, so it feels like they are making a choice too, and they are! Having a few ideas to choose from is always better than just throwing spaghetti at the wall and seeing what sticks.
Think of the larger areas of action like hotels, catering, decor and music as subheadings for planning. Then collaboratively conquer each to-do with the one or two people assigned to that area. You can do this with or without a planner involved. A great wedding planner is able to navigate multiple relationships with you that may all funnel into the planning of one wedding, to help you stay sane, organized and cohesive.