I'd set up the business as an LLC, which would define the capital each party would put into the partnership the work each party will do and the ownership each party will have of the partnership. The ownership shares should reflect how you want decisions to be made. If one person will be making the decisions then they should have over 50% share. It is really dangerous to have a family business where everyone has to agree, in order to get something done. Someone needs to manage the business and be in charge.
Then, I would write up an operating agreement that puts down on paper how each player gets compensated for their work. (Dollars per hour, competitive quote before work begins... whatever you want). This does not need to really be a legal document, just an agreement that everyone signs that sets the ground rules. Then when there is a disagreement you can all go back to the original agreement that everyone has.
Then just run the LLC as a business and pay people based on what you've all agreed to.