you should not ask him how to entertain his parentsYou 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...
他父母在中国有亲戚的,还是很有钱的亲戚,而且他父母都去中国旅行过好几次
可是他妈妈曾经亲口对我说,中国的土豆不好吃,中国的什么什么什么都不好。。。我忍住没有发飚。。。