In such stories, I am always amazed how blind relatives are. They knew that kidnapper for ages, they new his behaviour, thoughts (it is not hard to predict elder peoples intentions and moves, as with age, they turn to more and more to children like), they probably knew his addiction to gambling. I mean they could have foreseen that grandpa is intend to do something weird. I see one major problem here - why Yuan family did not do anything with his gambling addiction?
Yes, the role of the family also plays an important role in cases like this, they cannot remain silent when they see the strange behavior of one of their families. And if they see something strange and they continue to let it go, then I think the family also had a hand in the "crimes" committed by the family itself. A good approach from the family, in my opinion, can make them realize that what their family members are doing is wrong and this is where we really have to be sensitive to the environment around us, don't let us ignore something that is taken for granted, because that will be disastrous later.