The startup has not been incorporated yet. It has 2 non technical- and non business-oriented co founders who thought of the original idea. They got government non-diluting grant of $50k, and they used it to develop a technological POC (paid to developrs), and submit a provisional documentation for a patent. They are looking for a CEO and a CTO to take it to the next stage (seed round, and getting to product-market fit). They will continue contributing to the company, but have no distinct role in its next phase. I have an experience of beening the the co founder and the CEO of a funded company.
The short, sweet answer is advice I got from a mentor: talk it out until you're all happy. But I would caution against joining a company with founders who want to be involved "but have no distinct role in its next phase." If as CEO you're helping the company to grow and creating a lot of value, you may come to resent the fact that you only got 1/3 (or 1/4) of the pie. Clearly defined job descriptions (and a new vesting schedule with a cliff for the original founders) can ensure that everybody stays hungry and works hard to make the company profitable.