The path is towards permanent residency, not citizenship.
It really makes no sense for︆ you to waste money by being employed by your father-in-law's company when you can simply︇ have the marriage visa, which allows you to stay indefinitely in Thailand, as long as︈ you stay married.
Also, if you're married and you really want a work permit, you︉ can create a company with your wife and hire yourself after hiring 2 Thai employees.︊ One of these employees can be your wife, hence in reality you only need to︋ hire one Thai employee.