You should try to observe and take action by yourself.
I think if the main problem is their lack of knowledge about China, tell them about it. Share some of your views on China with them. Or share what your family life is like with them. If they are completely uninterested in anything about China, well, just shut up and walk away...
If I were him, as a son, I would like my mum to know the pretty and lovely side of my gf, while I would like my gf to feel that my family welcome her...
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