It would be hard to tell if 12 lb is large for your little guy. Yorkies come in all sizes from the very tiny to larger. The easiest way to tell would be to see if you can easily feel his bones. If they are easily felt then 12 lbs is not too big. But if there if you have a hard time feeling them he could probably loose a little weight. I'm going to guess that he is probably overweight being fed human food.
It is just not health to feed human food and you need to explain this to your dad. Mine are all in the 11 to 12 lb range but they are bigger yorkies. They eat about 1/4 cup of food twice a day. I try to limit their treats as well.
If he is not eating his food when you put it down then I would not leave it out for him. Pick it up and offer it at a later time. He will eat if you cut out the treats and other snacks that he is getting. Good luck and welcome to YT!
