Yorkies can be a little stubborn, can't they
It took us a while to get Romeo trained too! He's 10 months old now and really good! He knows when he poops/pees on the pads, is a good thing, and prances around proudly! Ofcourse we praise him, sometimes overpraise him! But it feels like winning the jackpot when he goes where he's supposed to!
Just be persistent and don't leave them somewhere where you can't see them, thats when they go
You have to keep a very close eye on them in the beggining and give it a few months. I know! It was crazy for us in the beggining!
But things will get better over time. They are very smart and will learn quickly but then you have to get them over their stubborness