How old are they? They can't usually hold their bladders through the night until 5 months of age. If they are over 5 months of age and they always pee on the pad, put the pad outside of the room they sleep in. Most likely, if they know they have to pee on the pad, they will hold until they see that pad!
If they are still under 5 months, a good method is to use the crate. Keep them in the crate all night long. They don't usually pee in the place they sleep. In the morning, take them to the pad (or outside). They start to catch on...
If you want them to eventually go potty outside, put the pad by the nearest exit in the house - it will make your life a lot easier because you will know when they have to go potty.
One last thing...I know some people do not agree with this since yorkie's are so small, but I have a 6 month 11 pound yorkie and I live in the city with few big birds so I have a doggy door. That was the best thing that ever happended our house. Now I don't have to worry about potty mistakes. My Stomper boy ALWAYS goes outside. I still give him treats when I see him go potty outside. I'll probably do that until he is 1 years old to make sure he is fully potty trained!
Good luck!!!
__________________  Kimberly & Stomper |