Generally it's not uncommon for companies to be started by licensing existing patents from other companies. The nature of that license matters more than who own

Generally it's not uncommon for companies to be started by licensing existing patents from other companies. The nature of that license matters more than who owns it - things like how long it will last, what you can and can't do, do you have exclusive rights, etc. I am curious who paid for the patent application. Usually this is a lengthy and expensive process. I am also assuming that the inventor was employed somewhere while they developed this stuff - have the employers signed away their rights to the IP? I would also point out that patents on their own are basically worthless. They do not protect small startups from being copied because you cannot afford to sue a competitor. At best they are a signal to investors that what you have invented is sufficiently unique as to pass a patent search, but even that is not saying a whole lot. In short, I think the patent itself is a secondary issue. The problem seems to be a lack of incentive alignment between the founders. I would also suggest you look into some of the issues I've stated above, such as who the assignee currently is, who the co-inventors are, if there are any other parties who could have claims over it. This I see as a potentially bigger problem.