You are wise to consider this ahead of time. Looks like you are getting lots of good suggestions. I had a one year old Lhasa Apso when my first son was born (over 30 years ago). I did not think ahead and it was not a good experience. First, the Lhasa Apso kept leaving a little pile under the crib every day. I put up a doggy gate so he could not go in the room and he started leaving the little pile in the hallway outside the room. This all got him scolded which probably increased the resentment. He would growl when we were holding my son and I never dared leave them together in a room without us. I finally gave up and found a new home for the dog, who was really just a puppy himself. But maybe with the right forethought, I could have helped him with the transition.
On the plus side, Yorkies seem to be the most loving dogs I have ever come across. It is almost like they are their own little species and not really a dog at all. I think they might deal with the arrival of a new baby as just another person to love on them.
Congratulations on your upcoming baby arrival!