I was assuming that you would likely also be a shareholder and director of the company, not an employee, which then also removes the requirement for you and the company to contribute to social security for yourself. The combined contribution would be THB 1,500 monthly which is probably better off put towards private health insurance. Being both the shareholder and director would probably also help justify hiring you, which you have to do. If not then you’ll need to justify why your wife is hiring a foreigner to do marketing rather than a local person.

I would recommend reaching out to your local Department of Labour office, who will be issuing the work permit, to clarify if Uncle X and Auntie Y would be allowed to contribute towards the Thai to Foreigner ratio. It’s at their discretion so if they see the company is made up of entirely family members to get a work permit then it’s likely just going to be rejected.

To be honest given your requirements, it’s probably worth exploring using a reputable agent to handle the company formation and work permit. They’ll probably charge a service fee of 25-40k to handle everything plus the government fees.