I have a work permit (issued under the BOI scheme) My adopted son is starting a coffee shop in the shop downstairs, even though I have paid for everything I will not be working in the shop when it starts trading. He will be getting his girl friend to help him and being typical Thai does not want to register the business.

Should I add this to my existing work permit (or in fact can I) if the business is a small family unregistered one?

Any advise would be appreciated as I don't want immigration or police sniffing around.

Ownership does not require a work permit, working in the shop will require a work permit but is not your intention. But do not sign any documents, let your adopted son do that as manager.