Wow, tough situation, tough question to be asking. There isn't a book somewhere that has this kind of thing written down. Ownership normally starts with shares, like shares of stock, even in small businesses. There are no formulas.
You should probably be talking about this to an attorney.
The more you plan ahead, learn about the successes and failures of other business leaders while simultaneously creating an agile, easily adaptable company, the more likely you are to pass new milestones seamlessly.