Well it sounds to me like you love him and really that is all that matters. Are you positive that he is really only 12 weeks old? If you feel that your cousin coworker was not truthful about the parents both being full Yorkie maybe you also didn't get truthful information about his age as well. Did the vet take a guess what they thought he might be mixed with? Just because he is bigger does't necessarily mean he is not full Yorkie. My Pebbles is 11 lbs of Yorkie lovin'.
I'm so glad that you have fallen in love with Charlie even though it is obvious that he will be a larger pup when fully grown. I would love to see pictures of the little man.
There are people that come to YT every day with the idea to breed, breeding emergencies, money making from breeding ideas, and sadly those with very sick puppies from poor breeding and to some of us it is all pretty shocking. Others come worried that about something as simple as how big their puppy is going to be and I am glad that you do not feel this way about Charlie. It is always nice to hear that what is said on YT is being heard and that some are listening and learning. Enjoy your puppy and show us some pictures already