You would need some type of disinterested, but experienced, mediator. This could be a CPA or financial advisor experienced in family negotiations. I agree with Craig that you don't need to use a corporation, but I imagine that was just a phrase you used to represent the organization. How you set it up will depend upon what you are trying to accomplish and the purpose of the organization. A CPA and/or financial advisor and/or tax attorney would be able to help with this.
Good luck and I hope this helps!