Boy, I am torn on this one. Ronnie is right, have them meet other small dogs and animals.
I remember a story, I think it was on this forum, years and years ago about a man who had Newfs and a Yorkie. The dogs had lived together for a long time. One day, I think it was on a beach, one of the Newfs playfully picked up the Yorkie and shook it like a toy. Killed the Yorkie. So sad, and it stuck in my mind.
That may have been just a fluke, but I also took in a Newf rescue once, who was very sweet, tolerant, but energetic. Had her for 7 months as she needed a lot of obedience training to quell her enthusiasm. I also had two Newfs of my own and my parents ancient Schnauzer, and my son's Siberian Husky. The Schnauzer would go into a frenzy when the other dogs played. She would bark and charge them, snapping her teeth. The big dogs were always tolerant of this, but one day, the rescue finally had enough of the bad behavior from the Schnauzer and tried to discipline her. She ended up bruising the Schnauzer badly. If the little dog had been bigger, it would have been OK, but she was so little, she got injured.
I think these are two isolated cases, but I thought you should know. Yorkies are very delicate dogs, so my advice would be to supervise carefully until you are confident that they will be OK together. But just keep in mind that it doesn't take much to hurt a tiny dog.