Tip-toe carefully here. Some questions: Is this business incorporated? If so what is your share capital position? Is there a well written business plan accompanied with proffessionally reviewed financials? Who sits on the Board of Directors? How are the business decisions made within the Company/Partnership? How is conflict resolution managed? WHO is the final desicion maker when it comes down to needing to make a potentially unpopular stratigic desicion? What happens when the new business needs more money (normal situation for a young business?) Who decides when to either issue dividends back to the 'shareholder-partners' or instead (perhaps) plow all the profits back into the business? What kind of access do you have to the financial books? Monthly, quarterly annually? What if your relatives aren't running the business well ..... What is the method to replace family managers with (if needed) non-family professionals?
As far as the precentage of ownership question it has allot to do with whether the other owners are taking a salary and/or making more 'work' decisions.
In my opinion NEVER go into a partnership. Create a limited or incorporated company to provide some legal structure AND protect you personally. In the food industry all you need is one food posioning to reach deep thru the business veil direct to the actual owners in a lawsuit. Not to mention the pockets of emotional 'quicksand' in working with family in business. No matter these are just my thoughts.....Good Luck with your venture.