Little Dog House Training. HELP!

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So I'm an animal person and a complete sucker. Normally, I stick to big dogs. Big as in 60 pounds used to be the "small dog" in my house. Them this poor little Shihtzu was wondering alone on the highway. I couldn't very well leave him there, so I waded out into traffic and brought him home. After a month of searching for his owners, he had grown on me, and now he is The Jinx! Now, as I said, I don't normally do little dogs, but The Jinx wormed his little way into my heart and I adore him. But I have 100 pound plus dogs and despite my best efforts, Jinx would get hurt while playing with them. So I found a second little dog, my MiaMia. I adore them both. They are the sweetest most snuggly little teddy bears you could ever hope for and I wouldn't give them up for the world. However they are absolutely ruining my carpets by their refusal to house train. No amount of begging, treats, pleading crating, leashing, or screaming has deterred them or encouraged them to learn what my big dogs had down pat in a matter of a week at most. So can someone out there who has a lifelong knowldge of little stubborn cute dogs please give me a clue as to what I'm doing wrong???