A lot of times with Vietnamese families like this, they will tend to deny that the person actually lives there or he is currently not home. All Charles needed to say to family when they pick up the phone is something like, "if someone ask for me, tell them that i moved out or you don't know who i am, or that i am not home----Because this person that is calling me is from school and he's really bugging me about ----." Just something as simple as that, and i think Charles will get the validation from his family. I don't think his whole family is part of a big family scam scheme, otherwise the house, the cars, everything they have, would probably out of scamming people? If that is so, they would have been track down long time ago.
What you can try is calling the house again and ask for an elder around the house, and in this case i suspect Lan to be the "mom" of the house. First time, you can tell her sincerely what happened and see how she responds. If it doesn't work, try again another time and say that you are from some company etc. or even SJ police department looking for Charles and tell her you need to get a hold of him. If she said she doesn't know him or if the name Charles doesn't ring a bell, ask her if any member plays tennis. Tell her that the police is conducting an investigation and if you can't get a hold of him, some serious sh%t going happen.
Call again another time and repeat. You might be able to squeeze something out when you struck some fear. It sucks to do it to them but it also suck that you're getting scam. None of it would of taken place if the dude just send you the ish.
It will be funny if Charles is reading this and aware of what you're trying to do and take it lightly, but wait until the real SJPD call, what will you say to your family members? "The SJPD is bugging me...tell them to bug off"?