Vixen
Penultimate Amazing
Could you explain this to us simple folk. What is the difference between coming by a part of your ancestry "by blood" and "through marriage"? There is no difference from what I can see. "Blood" ties are merely family/parental ties and being married or not makes no never mind. Unless you're talking about the current generation, those old marriages make up "blood" ties. (Current generation, obviously... I'm married to a Thai; I do not claim Thai ancestry. My son, however, is American-Thai. Are you claiming that his claim on Thainess is not legitimate because his daddy married into it? That makes no sense.)
Your son is Thai, his cousin on your US side probably is not. His second cousin on the US side, almost certainly not.