I had to laugh when reading your post. They are the worst at housebreaking I agree. The advice given so far is very good. Leashing them to you really helps and confining them to a small area is very helpful. My Zoey is three years old and every time she poos on her pad she runs to me very hyper and I get loud and tell her what a good girl she is. This makes her very happy and me too. Hang in there and be consistent and your little one will reward you with so much love and joy. Just a word of caution - be careful with the bigger dogs playing rough with your yorkie. Their bones break very easily.
__________________  RIP my darling little Gina |